freedm: Remove override for menu skull.

FreeDM had a special override to use an animated rocket for the menu
selector, a tweak to make it more deathmatch-appropriate. Unfortunately
the rocket animation is too wide and causes Chocolate Doom to error out
when the help screen is brought up (F1) with "Bad V_DrawPatch". Even if
the horizontal offset is adjusted it will overlap with parts of the help
screen and obscure them. I think the easiest solution is to just remove
the override.

buildcfg.txt

@@ -770,13 +770,8 @@ M_RDTHIS	0	0
 M_OPTION	0	0
 M_QUITG	0	0
 M_NGAME	0	0
-#ifdef FREEDM
-M_SKULL1 = m_rokt1    16     -4
-M_SKULL2 = m_rokt2    16     -4
-#else
 M_SKULL1	0	-1
 M_SKULL2	0	-1
-#endif
 M_THERMO	-2	-1
 M_THERMR	0	0
 M_THERMM	0	0