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/cave/groudon.pal

@@ -1,51 +0,0 @@
-JASC-PAL
-0100
-48
-0 0 0
-246 246 189
-222 213 106
-180 156 106
-197 172 123
-205 189 115
-213 197 148
-197 172 106
-230 222 172
-255 189 49
-238 230 123
-213 115 32
-222 172 106
-230 197 139
-230 213 156
-238 230 180
-0 0 0
-246 246 189
-222 213 106
-180 156 106
-197 172 123
-205 189 115
-213 197 148
-197 172 106
-230 222 172
-255 189 49
-238 230 123
-82 106 172
-148 156 164
-197 189 164
-230 213 180
-238 230 180
-0 0 0
-106 74 65
-148 115 82
-180 139 90
-213 180 131
-230 213 156
-0 0 0
-205 148 74
-230 156 57
-255 172 49
-255 189 49
-205 148 74
-205 148 74
-0 0 0
-0 0 0
-0 0 0

graphics/battle_terrain/cave/palette.pal

@@ -1,51 +0,0 @@
-JASC-PAL
-0100
-48
-0 0 0
-197 180 131
-205 197 90
-164 139 90
-180 156 106
-189 172 98
-189 164 115
-180 156 90
-197 164 115
-189 172 98
-222 213 106
-172 139 82
-180 148 98
-189 156 106
-197 164 106
-197 172 115
-0 0 0
-197 180 131
-205 197 90
-164 139 90
-180 156 106
-189 172 98
-189 164 115
-180 156 90
-197 164 115
-189 172 98
-222 213 106
-172 139 82
-180 148 98
-189 156 106
-197 164 106
-197 172 115
-0 0 0
-106 74 65
-148 115 82
-180 139 90
-213 180 131
-230 213 156
-0 0 0
-180 139 90
-180 139 90
-180 139 90
-213 180 131
-106 74 65
-148 115 82
-0 0 0
-0 0 0
-0 0 0