Increase maximum skin count to 255

This time without spare slots, because I don't see shenanigans like
WAD_MUSIC happening with skin indices. Verified to work by saving a
replay with 139 skins as the 133th skin and playing it back a few times.
Shouldn't cause issues with netcode either because there are no SINT8s
handling skin indices.

src/doomdef.h

@@ -227,7 +227,7 @@ extern char  logfilename[1024];
 // NOTE: it needs more than this to increase the number of players...
 
 #define MAXPLAYERS 16
-#define MAXSKINS 128
+#define MAXSKINS 255
 #define PLAYERSMASK (MAXPLAYERS-1)
 #define MAXPLAYERNAME 21