Use factorial rather than numeric_fac in create_operator.sql.

Use factorial rather than numeric_fac in create_operator.sql.

These two SQL functions are aliases for the same C function, so this
change has no semantic effect.  However, because we dropped the
numeric_fac alias in HEAD (commit 76f412ab3), operator definitions
based on that one don't port forward, causing problems for cross-version
upgrade tests based on the regression database.

Patch all active back branches to dodge the problem.

Discussion: https://postgr.es/m/449144.1600439950@sss.pgh.pa.us