Remove links in changelog to github milestones that no longer exist (#1415)

Author: ianthomas23

CHANGELOG.md

@@ -1669,8 +1669,6 @@ failures in nbconvert.
 
 5.1.0 fixes some important regressions in 5.0, especially on Windows.
 
-[5.1.0 on GitHub](https://github.com/ipython/ipykernel/milestones/5.1)
-
 - Fix message-ordering bug that could result in out-of-order
   executions, especially on Windows [#356](https://github.com/ipython/ipykernel/pull/356)
 - Fix classifiers to indicate dropped Python 2 support
@@ -1683,17 +1681,13 @@ failures in nbconvert.
 
 ### 5.0.0
 
-[5.0.0 on GitHub](https://github.com/ipython/ipykernel/milestones/5.0)
-
 - Drop support for Python 2. `ipykernel` 5.0 requires Python >= 3.4
 - Add support for IPython's asynchronous code execution
   [#323](https://github.com/ipython/ipykernel/pull/323)
 - Update release process in `CONTRIBUTING.md` [#339](https://github.com/ipython/ipykernel/pull/339)
 
 ## 4.10
 
-[4.10 on GitHub](https://github.com/ipython/ipykernel/milestones/4.10)
-
 - Fix compatibility with IPython 7.0 [#348](https://github.com/ipython/ipykernel/pull/348)
 - Fix compatibility in cases where sys.stdout can be None
   [#344](https://github.com/ipython/ipykernel/pull/344)
@@ -1702,8 +1696,6 @@ failures in nbconvert.
 
 ### 4.9.0
 
-[4.9.0 on GitHub](https://github.com/ipython/ipykernel/milestones/4.9)
-
 - Python 3.3 is no longer supported [#336](https://github.com/ipython/ipykernel/pull/336)
 - Flush stdout/stderr in KernelApp before replacing
   [#314](https://github.com/ipython/ipykernel/pull/314)
@@ -1717,15 +1709,11 @@ failures in nbconvert.
 
 ### 4.8.2
 
-[4.8.2 on GitHub](https://github.com/ipython/ipykernel/milestones/4.8.2)
-
 - Fix compatibility issue with qt eventloop and pyzmq 17
   [#307](https://github.com/ipython/ipykernel/pull/307).
 
 ### 4.8.1
 
-[4.8.1 on GitHub](https://github.com/ipython/ipykernel/milestones/4.8.1)
-
 - set zmq.ROUTER_HANDOVER socket option when available to workaround
   libzmq reconnect bug [#300](https://github.com/ipython/ipykernel/pull/300).
 - Fix sdists including absolute paths for kernelspec files, which
@@ -1734,8 +1722,6 @@ failures in nbconvert.
 
 ### 4.8.0
 
-[4.8.0 on GitHub](https://github.com/ipython/ipykernel/milestones/4.8)
-
 - Cleanly shutdown integrated event loops when shutting down the
   kernel. [#290](https://github.com/ipython/ipykernel/pull/290)
 - `%gui qt` now uses Qt 5 by default rather than Qt 4, following a
@@ -1747,8 +1733,6 @@ failures in nbconvert.
 
 ### 4.7.0
 
-[4.7.0 on GitHub](https://github.com/ipython/ipykernel/milestones/4.7)
-
 - Add event loop integration for `asyncio`.
 - Use the new IPython completer API.
 - Add support for displaying GIF images (mimetype `image/gif`).
@@ -1762,17 +1746,13 @@ failures in nbconvert.
 
 ### 4.6.1
 
-[4.6.1 on GitHub](https://github.com/ipython/ipykernel/milestones/4.6.1)
-
 - Fix eventloop-integration bug preventing Qt windows/widgets from
   displaying with ipykernel 4.6.0 and IPython ≥ 5.2.
 - Avoid deprecation warnings about naive datetimes when working with
   jupyter_client ≥ 5.0.
 
 ### 4.6.0
 
-[4.6.0 on GitHub](https://github.com/ipython/ipykernel/milestones/4.6)
-
 - Add to API `DisplayPublisher.publish` two new fully
   backward-compatible keyword-args:
 
@@ -1815,15 +1795,11 @@ failures in nbconvert.
 
 ### 4.5.2
 
-[4.5.2 on GitHub](https://github.com/ipython/ipykernel/milestones/4.5.2)
-
 - Fix bug when instantiating Comms outside of the IPython kernel
   (introduced in 4.5.1).
 
 ### 4.5.1
 
-[4.5.1 on GitHub](https://github.com/ipython/ipykernel/milestones/4.5.1)
-
 - Add missing `stream` parameter to overridden
   `getpass`
 - Remove locks from iopub thread, which could cause deadlocks during
@@ -1834,8 +1810,6 @@ failures in nbconvert.
 
 ### 4.5.0
 
-[4.5 on GitHub](https://github.com/ipython/ipykernel/milestones/4.5)
-
 - Use figure.dpi instead of savefig.dpi to set DPI for inline figures
 - Support ipympl matplotlib backend (requires IPython update as well
   to fully work)
@@ -1847,15 +1821,11 @@ failures in nbconvert.
 
 ### 4.4.1
 
-[4.4.1 on GitHub](https://github.com/ipython/ipykernel/milestones/4.4.1)
-
 - Fix circular import of matplotlib on Python 2 caused by the inline
   backend changes in 4.4.0.
 
 ### 4.4.0
 
-[4.4.0 on GitHub](https://github.com/ipython/ipykernel/milestones/4.4)
-
 - Use
   [MPLBACKEND](http://matplotlib.org/devel/coding_guide.html?highlight=mplbackend#developing-a-new-backend)
   environment variable to tell matplotlib >= 1.5 use use the inline
@@ -1889,8 +1859,6 @@ failures in nbconvert.
 
 ### 4.3.0
 
-[4.3.0 on GitHub](https://github.com/ipython/ipykernel/milestones/4.3)
-
 - Publish all IO in a thread, via `IOPubThread`. This solves the problem of requiring
   `sys.stdout.flush` to be called in
   the notebook to produce output promptly during long-running cells.
@@ -1913,22 +1881,16 @@ failures in nbconvert.
 
 ### 4.2.2
 
-[4.2.2 on GitHub](https://github.com/ipython/ipykernel/milestones/4.2.2)
-
 - Don't show interactive debugging info when kernel crashes
 - Fix handling of numerical types in json_clean
 - Testing fixes for output capturing
 
 ### 4.2.1
 
-[4.2.1 on GitHub](https://github.com/ipython/ipykernel/milestones/4.2.1)
-
 - Fix default display name back to "Python X" instead of "pythonX"
 
 ### 4.2.0
 
-[4.2 on GitHub](https://github.com/ipython/ipykernel/milestones/4.2)
-
 - Support sending a full message in initial opening of comms
   (metadata, buffers were not previously allowed)
 - When using `ipython kernel install --name` to install the IPython
@@ -1938,22 +1900,16 @@ failures in nbconvert.
 
 ### 4.1.1
 
-[4.1.1 on GitHub](https://github.com/ipython/ipykernel/milestones/4.1.1)
-
 - Fix missing `ipykernel.__version__` on Python 2.
 - Fix missing `target_name` when opening comms from the frontend.
 
 ### 4.1.0
 
-[4.1 on GitHub](https://github.com/ipython/ipykernel/milestones/4.1)
-
 - add `ipython kernel install` entrypoint for installing the IPython
   kernelspec
 - provisional implementation of `comm_info` request/reply for msgspec
   v5.1
 
 ## 4.0
 
-[4.0 on GitHub](https://github.com/ipython/ipykernel/milestones/4.0)
-
 4.0 is the first release of ipykernel as a standalone package.