Drop unused Python 3.7 compatibility code (#406)

Now that Python 3.8 is the minimum supported version, there is no need
for this `typing_extensions` branch or a dependency on
`typing-extensions`. So drop both to cleanup the code. Also should bring
coverage back up.

Author: jakirkham

docs/release.rst

@@ -44,7 +44,7 @@ Maintenance
   By :user:`Dimitri Papadopoulos Orfanos <DimitriPapadopoulos>`, :issue:`369`.
 
 * Drop Python 3.7.
-  By :user:`John Kirkham <jakirkham>`, :issue:`405`.
+  By :user:`John Kirkham <jakirkham>`,, :issue:`405` :issue:`406`.
 
 * Test with zfpy 1.0.0.
   By :user:`John Kirkham <jakirkham>`, :issue:`385`.

numcodecs/ndarray_like.py

@@ -1,10 +1,4 @@
-import sys
-from typing import Any, Dict, Optional, Tuple, Type
-
-if sys.version_info >= (3, 8):
-    from typing import Protocol, runtime_checkable
-else:
-    from typing_extensions import Protocol, runtime_checkable
+from typing import Any, Dict, Optional, Protocol, Tuple, Type, runtime_checkable
 
 
 class _CachedProtocolMeta(Protocol.__class__):

pyproject.toml

@@ -17,7 +17,6 @@ readme =  "README.rst"
 dependencies = [
     "entrypoints",
     "numpy>=1.7",
-    "typing-extensions>=3.7.4"
 ]
 requires-python = ">=3.8"
 dynamic = [