Delete the ext.vector.footerCleanup module

An experimental module whose functionality has been now imported into
MediaWiki core and the WikiEditor extension.

Related changes: I1b924999, Id9269876, I36ecd06b.

Bug: 43689
Change-Id: I1672a830dc5e2c9a5e95b76f1618b57aaa252c55
Merge "Delete the ext.vector.footerCleanup module"