Don't duplicate packages across requirements files

- Remove "gitdb" from test-requirements.txt, because it already a
  dependency of the project (listed in requirements.txt, which is
  used to build the value passed for install_requires in setup.py).

- Remove "black" from requirements-dev.txt, because it is listed in
  test-requirement.txt (which requirements-dev.txt sources).

Author: EliahKagan

requirements-dev.txt

@@ -4,7 +4,6 @@
 # libraries for additional local testing/linting - to be added to test-requirements.txt when all pass
 
 flake8-type-checking;python_version>="3.8"      # checks for TYPE_CHECKING only imports
-black
 
 pytest-icdiff
 # pytest-profiling

test-requirements.txt

@@ -11,5 +11,3 @@ pytest
 pytest-cov
 coverage[toml]
 pytest-sugar
-
-gitdb