Unpit lit version from setup.py (llvm#54)

We install lit via `tox` when we run the tests -- there is no need to
install `lit` when we only want to install LNT itself, and even less
of a need to pin it to a specific version (which in this case is old
and causes a bunch of tests to fail).

Author: ldionne

setup.py

@@ -132,7 +132,6 @@
         "click==6.7",
         "pyyaml==5.1.2",
         "requests",
-        "lit==0.11.1",
         "certifi"
     ],