(D7 backport) Deprecate RIGHT JOINs, because SQLite doesn't support them

This issue is for backporting #2011500: Deprecate RIGHT JOINs, because SQLite doesn't support them. to Drupal 7. Might not use the exact same wording as the committed Drupal 8 patch, but the key point is to indicate that it is deprecated (and especially that it should not be used on any code that needs to run on SQLite).