DB/Orgrimmar: More cleanup & name a phase - #32002

Changes proposed:

• Name phase 5509 as Legion Intro - Fate of the Horde gathering.
• Update the spawn positions and phase for creatures that were falling through the ground in the Orgrimmar Embassy.
• Update existing gameobject phases and spawn positions, and remove deprecated spawns.
• Move the remaining NPCs in Orgrimmar Embassy into phase 5509 without otherwise updating them. Note: Phase 5509 is still missing a number of spawns across the rest of Orgrimmar. This PR only covers the current spawns that are in the DB; the remaining phase work will be revisited at a later date - Soon™.

Tests performed:
Tested ingame