mediawiki.log: Do not dynamically redefine mw.log.deprecate

There's very little gain in doing it and it's annoying for static code
analysis and IDE-like functionality such as jumping to function
definition or listing all functions defined in a file.

Change-Id: Ida6c99539157de266c8e70eff344bd6491e39684
(cherry picked from commit dd813717156c6210cebb4f7692d6a41a606e9b8a)