Ensure mapping has no version_id_generator when checking missing version_id

Ensure mapping has no version_id_generator when checking missing version_id

Fixed 1.2 regression in ORM versioning feature where a mapping against a
:func:`.select` or :func:`.alias` that also used a versioning column
against the underlying table would fail due to the check added as part of
:ticket:`3673`.

See also #4194 and #4195 for related issues found regarding
mapped selects and versioning.

Change-Id: Ifabe9a5c8c1bfa72db5029faa7a5dbf71f0a7ca0
Fixes: #4193