changegroup: deduplicate 'getlocalchangegroup'
The two functions 'getlocalchangegroup' and 'getchangegroup' have been strictly
identical for multiple years ('getchangegroup' had a deprecated docstring)
We'll drop one of them (getlocalchangegroup, since it has the longest name).
However, we needs to migrate all users of the dropped one to the new one before
we can deprecate it. In the mean time we drop one of the duplicated definition
and the outdated docstring.
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
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commits you've made (for example, `python contrib/check-commit
273ce12ad8f1` will report some style violations on a very old commit).