configitems: drop the deprecated alias for commands.update.check
experimental.updatecheck was deprecated and should have been removed once 4.4
was released. Let's drop it now.
Differential Revision: https://phab.mercurial-scm.org/D3679
To run the tests, do:
cd tests/
python run-tests.py
See https://mercurial-scm.org/wiki/WritingTests for
more information on writing tests.