Migration step 148 will cause errors because we missed some
references to the columns being dropped. Removing the step
altogether causes problems with backwards compatibility tests
because the change already exists in the latest release tag.
To circumvent, we change v148 to an empty migration.
Add methods FindTable and RemoveColumn in private/dbutil/dbschema
Change-Id: Ia527e95b88a88c5dc82800928ce6f8cfb879e334
