RevisionIdentifier.getDefaultInstance() is static

This fixes warnings about static method being invoked on an instance,
plus it removes the now-unused instance.

Change-Id: I7c4594908d6b3a5c10e9b3f12e32ca203d3aa3d2
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "RevisionIdentifier.getDefaultInstance() is static"