Set icon directly in some PHUIButtonViews; drop PHUIIconView calls
Summary: Replace unneeded explicit `id(new PHUIIconView())` calls within `id(new PHUIButtonView())->setIcon()` by simply passing the FontAwesome icon namely directly.
Test Plan:
* Set up a Dashboard Query Panel and go to it, see that the "View All" header button of the "... Query Panel" box still renders the same icon.
* Set up a Project with a Milestone and a Subproject and go to its project profile page, see that the "View All" header button of the "Recent Activity", "Milestones" and "Subproject" boxes still render the same icon.
* Set up a User and go to their user profile page, see that the "View All" header button of the "Recent Activity" box still renders the same icon.
Reviewers: O1 Blessed Committers, valerio.bozzolan
Reviewed By: O1 Blessed Committers, valerio.bozzolan
Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Differential Revision: https://we.phorge.it/D26333