Comment, remove, or revise many unreferenced labels

[Rangi42]

These were found via unref.py: https://pastebin.com/airBsQbQ There are probably more that it didn't catch.

Some WRAM labels are not directly referenced but refer to used space, like individual struct fields; those shouldn't be commented.

This syncs with pret/pokegold#64.

[entrpntr]

Had a bunch more, but most appear to be addressed by the latest commit. I think this is all I see left (in 3 broad categories):

1. Should be commented as unreferenced? (all from engine/gfx/pic_animation.asm; not familiar with this part of pokecrystal, but they seem to be so?)

   • AnimateMon_Menu
   • AnimateMon_Trade
   • AnimateMon_Evolve
   • AnimateMon_Hatch
   • AnimateMon_HOF

2. Could be converted to comments:

   • BattleTowerTrainer[1-70]DataTable
   • BattleTowerMons[1-10]

3. Miscellaneous (applies to both pokecrystal/pokegold):

   • Could combine SGBBorderMap+SGBBorderPalettes under 1 label? (like with ChrisCard+ChrisPic -> ChrisPicAndTrainerCardGFX in pokegold)
   • Could add assert of some sort before cp TrophyIDs - DecorationIDs in engine/link/mystery_gift.asm? (like with BoxNameInputUpper - NameInputUpper, since TrophyIDs only purpose seems to be in offset calculation?)

[Rangi42]

AnimateMon_* are all referenced by the pokeanim macro. I've applied the rest of your comments. Thanks!

[Rangi42]

Since this already started using assert, I went ahead and added more. There may be other places where assertions are appropriate, but this covers the basics that #706 listed.