Don't show Space monograms in SpaceContextView

Summary: Ref T8449. Get rid of the S123 stuff in headers, it feels like clutter.

Test Plan: Looked at objects in Spaces.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T8449

Differential Revision: https://secure.phabricator.com/D13243