Merge AphrontSideNavView into AphrontSideNavFilterView

Summary: After D4034 there are no AphrontSideNavView callsites outside of AphrontSideNavFilterView.

Test Plan: Looked at about a million side navs.

Reviewers: chad

Reviewed By: chad

CC: aran

Maniphest Tasks: T1960

Differential Revision: https://secure.phabricator.com/D4035