[Tools] Remove scm-remove-wrong-checkout.py.

It has served us well, but since its introduction gclient itself has
developed similar capabilities, but instead of bluntly removing
checkouts with the "wrong" SCM, it moves them to a separate _bad_scm/
directory, which is safer and preserves any local changes one might have
around.
Merge pull request #2087 from rakuco/remove-scm-remove-wrong-checkout

[Tools] Remove scm-remove-wrong-checkout.py.