[nova][train] Remove deprecated RetryFilter

Affects config with Blazar and fake Nova only.
The default does not include it.

Upstream docs:
RetryFilter - Deprecated since version 20.0.0 (Train)
Since the 17.0.0 (Queens) release, the scheduler has provided
alternate hosts for rescheduling so the scheduler does not need to
be called during a reschedule which makes the RetryFilter useless.

Change-Id: I26bf45997005124e9166b5bf1d44cb276624430b