mediawiki.page.watch.ajax: Don't use deprecated tooltipAccessKeyRegexp

Remove dependency on 'mediawiki.page.startup' since this is no
longer needed (it was there to ensure mw.util.init, which used to
populate mw.util.tooltipAccessKeyRegexp, ran first).

Change-Id: Iceecc228bce676de84de35220fa4d217be0f0b75
Merge "mediawiki.page.watch.ajax: Don't use deprecated tooltipAccessKeyRegexp"