Remove get_instance_type and get_active_by_window from nova compute API

Commit 013b301c1c makes both methods vestigial since the
simple_tenant_usage API was the only thing using them.

Change-Id: Idbe8183760edd57b58564761c30f2f6e3ad0086e
Merge "Remove get_instance_type and get_active_by_window from nova compute API"