remove silenced warnings that were not triggered anyways

line length comes from @tw - i would prefer 80 columns personnally, but don't want to argue over that bikeshed

the 120 limit *does* trigger warnings right now, but it's better to do that than to make the problem worse for future PRs

setup.cfg

@@ -2,7 +2,5 @@
 python_files = testsuite/*.py
 
 [flake8]
-ignore = E226,F403
-max-line-length = 250
-exclude = docs/conf.py,borg/_version.py,build,dist,.git,.idea,.cache
-max-complexity = 100
+max-line-length = 120
+exclude = build,dist,.git,.idea,.cache,.tox