Merge battle graphics into battle_terrain and remove un-included files

The previous battle folder contained the used (and until recently undocumented) battle terrain graphics, while everything in the previous battle_terrain folder contained unused data (which is now at battle_terrain/unused, minus the files that never get included in the rom).

graphics/battle_terrain/water/kyogre.pal

@@ -1,51 +0,0 @@
-JASC-PAL
-0100
-48
-0 0 0
-246 246 189
-90 148 222
-148 213 238
-180 222 222
-106 172 230
-172 213 213
-123 189 230
-205 222 197
-0 0 0
-0 0 0
-172 139 82
-189 156 106
-213 197 148
-230 213 164
-238 230 180
-0 0 0
-246 246 189
-90 148 222
-148 213 238
-180 222 222
-106 172 230
-172 213 213
-123 189 230
-205 222 197
-0 0 0
-0 0 0
-172 139 82
-189 156 106
-213 197 148
-230 213 164
-238 230 180
-0 0 0
-98 164 230
-131 197 255
-172 238 255
-255 255 255
-205 255 255
-0 0 0
-0 0 0
-0 0 0
-0 0 0
-0 0 0
-0 0 0
-0 0 0
-0 0 0
-0 0 0
-0 0 0

graphics/battle_terrain/water/palette.pal

@@ -1,51 +0,0 @@
-JASC-PAL
-0100
-48
-0 0 0
-255 255 255
-90 148 222
-148 213 238
-180 230 246
-106 172 230
-197 238 255
-123 189 230
-222 246 255
-0 0 0
-0 0 0
-205 222 246
-222 230 238
-230 238 238
-238 246 246
-246 246 255
-0 0 0
-255 255 255
-90 148 222
-148 213 238
-180 230 246
-106 172 230
-197 238 255
-123 189 230
-222 246 255
-0 0 0
-0 0 0
-205 222 246
-222 230 238
-230 238 238
-238 246 246
-246 246 255
-0 0 0
-0 0 0
-0 0 0
-0 0 0
-197 238 255
-148 213 238
-123 189 230
-90 148 222
-49 106 189
-16 74 156
-0 0 0
-0 0 0
-0 0 0
-0 0 0
-0 0 0
-0 0 0