fix nits in Python tests causing build failure

[vladak]

Fixes the problem recently surfacing during Linux builds:

[INFO] --- exec:1.6.0:exec (Python flake8) @ tools ---
flake8.checker            MainProcess     93 INFO     Making checkers
flake8.main.application   MainProcess    756 INFO     Finished running
flake8.main.application   MainProcess    756 INFO     Reporting errors
flake8.main.application   MainProcess    757 INFO     Found a total of 13 violations and reported 2
/home/runner/work/opengrok/opengrok/tools/src/test/python/test_readconfig.py:40:12: E721 do not compare types, for exact checks use `is` / `is not`, for instance checks use `isinstance()`
/home/runner/work/opengrok/opengrok/tools/src/test/python/test_restful.py:33:55: E231 missing whitespace after ','
Error:  Command execution failed.

Also, remove the OldC ctags test. That parser was removed in Universal ctags in universal-ctags/ctags@4c7738d