contrib: remove check-code rule about indentation
We're moving towards a clang-format world, and clang-format is able to
wrap argument lists with spaces reliably, while still enforcing tabs
globally. Let's let clang-format do its job, and not do as much
C-style enforcement with regular expressions.
Differential Revision: https://phab.mercurial-scm.org/D1130
Our full contribution guidelines are in our wiki, please see:
https://www.mercurial-scm.org/wiki/ContributingChanges
If you just want a checklist to follow, you can go straight to
https://www.mercurial-scm.org/wiki/ContributingChanges#Submission_checklist
If you can't run the entire testsuite for some reason (it can be
difficult on Windows), please at least run `contrib/check-code.py` on
any files you've modified and run `python contrib/check-commit` on any
commits you've made (for example, `python contrib/check-commit
273ce12ad8f1` will report some style violations on a very old commit).