Remove flake8-tabs plugin that is incompatible with flake8 5

And instead manually ignore the relevant indentation errors/warnings.

setup.cfg

@@ -65,17 +65,17 @@ extend-exclude =
 
 # The following issues are ignored because they do not match our code style:
 ignore =
+	# These E1 checks report many false positives for code that is (consistently) indented with tabs alone.
+	E101, # indentation contains mixed spaces and tabs
+	E117, # over-indented
+	E126, # continuation line over-indented for hanging indent
 	E226, # missing whitespace around arithmetic operator
 	E261, # at least two spaces before inline comment
 	E501, # line too long
+	W191, # indentation contains tabs
 	W293, # blank line contains whitespace
 	W503, # line break before binary operator
 
-# flake8-tabs configuration
-use-flake8-tabs = true
-blank-lines-indent = always
-indent-tabs-def = 1
-
 [mypy]
 files=src/**/*.py
 python_version = 3.6

tox.ini

@@ -10,7 +10,6 @@ commands = python -m unittest discover --start-directory ./tests
 deps =
 	flake8 >= 3.8.0
 	flake8-bugbear
-	flake8-tabs
 commands = flake8
 
 [testenv:mypy]