Remove GET /projects/{project_id}/users (bug 1187257)

This resources was unimplemented in grizzly, and the semantics of the
call need to be carefully considered (and perhaps redesigned) prior to
implementation.

Change-Id: I34dcf10ad5536f22c350b33154d96fec78774d42
Merge "Remove GET /projects/{project_id}/users (bug 1187257)"