StaticModule: Remove unused GERRIT_UI_COOKIE
StaticModule: Remove unused GERRIT_UI_COOKIE

We only have one UI now. It's not impossible we'll want to switch UIs
again in the future, but at that point, adding a new constant will be
the least of our worries.

Change-Id: I6b3cab73a85247af71a67a2982e578d2100f17cc

GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit