Deprecate scheduler prep_resize

Scheduler prep_resize is no longer necessary as now the retries
from compute are going to the conductor.
Deprecating this method is also a prerequisite for the split
of the scheduler as it was issuing calls to computes.

Change-Id: I1092bbf7f541bb8cd7e33317f33b8c02761f284e
Merge "Deprecate scheduler prep_resize"