Re-write panels_update_7302() to not call panels_save_display()

Because panels_save_display() is called in panels_update_7302() it creates weird dependencies between update functions that we had to hack around in:

• #2786073: "Unknown column 'storage_type'" when updating from v3.3 to v3.6
• #2188277: "cache_panels doesn't exist" error on update

That update hook should operate directly on the database rather than calling that API function.

This will mostly involve copying the code from panels_save_display(), removing any cache clearing, and updating the database directly in such a way that it doesn't assume the columns based on the current 'panels_display' table schema -- it should only use columns that exist in the schema that's current as of when that update hook was written.