Drop "Quick Create" header from quick create menu

Summary:
Ref T9908. We can get a double-header with this ("Quick Create", "Create Task") which looks weird.

The behavior of this menu is probably obvious enough on its own from context and the "+" icon.

Test Plan: Opened menu, no more "Quick Create" item.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9908

Differential Revision: https://secure.phabricator.com/D14696