You can NOT delete commands from the drop-down list. You can only delete the Device/Activity Customize Buttons key mapping. The additional blank pages will go away after you move all key mapping upward (toward the first pages). Make sure you don't have an orphan key mapping past the first blank page.

Note: If you want to reduce the Receiver commands drop-down list, then add it with a fake model number forcing it to learn the list from your original remote (as if the device is not on the database). However, the original remote may be missing desirable commands that are available from the brand generic database, and compatible with your receiver.