This is a partial revert of commit 123631ad47.
Most of the logic was NOT reverted, just the part deleting the table was.
Note - this fix was done on integration.git and as a result no
upgrade step was added to re-introduce the table, sorry! This
means for those on integration.git you will have to re-install
your Moodle site so the 'message_popup' table is present.
Please see tracker for comments as to why we need to keep it! :)
Mark Nelson