Undo PokeCodec's PRs

This commit undoes most of PokeCodec's PRs after the debate in chat. Some
harmless or completely superseded PRs have been left alone, as there is not
much benefit in attempting to undo them.

Reverts #1104, #1108, #1115, #1118, #1119, #1124, #1126, #1127, #1132, #1136,
#1137, #1139, #1140, #1144, #1148, #1149, #1150, #1153, #1155, #1177, #1179,
#1180, #1181, #1182 and #1183.

constants/gba_constants.inc

@@ -26,9 +26,9 @@
 
 	.set OAM, 0x7000000
 
-	.set SOUND_INFO_PTR, IWRAM_END - 0x10
-	.set INTR_CHECK,     IWRAM_END - 0x8
-	.set INTR_VECTOR,    IWRAM_END - 0x4
+	.set SOUND_INFO_PTR, 0x3007FF0
+	.set INTR_CHECK,     0x3007FF8
+	.set INTR_VECTOR,    0x3007FFC
 
 	.set INTR_FLAG_VBLANK,  1 << 0
 	.set INTR_FLAG_HBLANK,  1 << 1