Only count bad refs when `moved` table exists (#23491)

Only count bad refs when `moved` table exists (#23491)

This keeps the logic to fail without upgrading when (A) there are bad rows and
(B) the "moved" table already exists. But we optimize so that we don't count
the bad rows unless the "moved" table is there. Previously we counted always,
but the first time a user attempts upgrade, the tables won't be there so
there's no point in counting.

Instead what we do is skip right to the CTAS, creating the _airflow_moved
tables. If there aren't any rows in the "moved" table, then we delete the table
immediately.

Also included here is a delete optimization, where we join to the moved table
instead of running the not exists query again.

Co-authored-by: Jed Cunningham <66968678+jedcunningham@users.noreply.github.com>
Co-authored-by: Ash Berlin-Taylor <ash@apache.org>