Remove Magma Emblem and Old Sea Map item icons

[SombrAbsol]

Since these items and their icons are not present in the game, there is not much point in keeping them in this repository. Confirmed by @GriffinRichards on the Discord server that the icon folder was a simple copy/paste from pokeemerald.

[GriffinRichards]

Their palettes should be removed as well https://github.com/pret/pokefirered/blob/master/graphics/items/icon_palettes/magma_emblem.pal https://github.com/pret/pokefirered/blob/master/graphics/items/icon_palettes/old_sea_map.pal

[SombrAbsol]

Thank you, I had forgotten them