Remove bogus Assert in foreign key cloning code

Remove bogus Assert in foreign key cloning code

This Assert was trying to ensure that the number of columns in the foreign
key being cloned was the same number of attributes in the parentRel.  Of
course, it's perfectly valid to have columns in the table which are not
part of the foreign key constraint. It appears that this Assert was
misunderstanding that.

Reported-by: Rajkumar Raghuwanshi
Reviewed-by: amul sul
Discussion: https://postgr.es/m/CAKcux6=z1dtiWw5BOpqDx-U6KTiq+zD0Y2m810zUtWL+giVXWA@mail.gmail.com