Remove setObjectName from PHUIHeaderView

Summary: This isn't used much (once?) and it's not needed. Fixes T8876

Test Plan: Grep for setObjectName and see if its PHUIHeaderView.

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T8876

Differential Revision: https://secure.phabricator.com/D13645