Compressing sidedefs can break both special effects and netgame syncing, so let's get rid of it

Launching SRB2 with the -compress parameter will make the game try to compress loaded maps by removing sidedefs it considers redundant. As the wiki has stated for years now, "this feature is unsupported and may end up removing sidedefs that were needed by a special effect". What's worse, it will completely break netgame synchronization if the host uses -compress and the client doesn't, or vice versa. So since this feature is causing problems and nobody is using it anyway, let's get rid of it.