Partially revert "Do not load "ext.wikiEditor.toolbar" if the user disabled WikiEditor"

The previous logic correctly matched the current behavior of these preferences
(which is described on bug 30795): Disabling "showtoolbar" does not disable WikiEditor,
so the ProofreadPage buttons should still be there in this case, for consistency.

This partially reverts commit Iaf19349ceb9a86e6d0fd117d1e3f3c70dbc632fb.

Change-Id: Id19b1c0ab5831f39f2707d69bde3909038e87054