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

mercurial/configitems.py

@@ -201,8 +201,6 b" coreconfigitem('commands', 'status.verbo"
 )
 coreconfigitem('commands', 'update.check',
     default=None,
-    # Deprecated, remove after 4.4 release
-    alias=[('experimental', 'updatecheck')]
 )
 coreconfigitem('commands', 'update.requiredest',
     default=False,