Support for changing the cinder periodic_interval config option
was added way back in havana as a workaround for bug #1180976
by change I20e52e66fcc94b224476cdd14c88bd6981b4e617. As the fix
for that bug does not require modifying this config value, and
such modification may have unintentional adverse effects, end
the support.
Change-Id: I1ef1fe564123216b19582262726cdb1078b7650e
Partial-bug: #1824837