Remove unused matha.S

Before commit a7d33b1c "(bug #3639) BoxOnPlaneSide rewrite" there
was more code here, but since then the only thing left is the
Invert24To16 function, to which I couldn't find any references since
the beginning of ioquake3's git history.

Resolves: https://github.com/ioquake/ioq3/issues/774
Signed-off-by: Simon McVittie <smcv@debian.org>

code/asm/matha.S

@@ -1,54 +0,0 @@
-/*
-===========================================================================
-Copyright (C) 1999-2005 Id Software, Inc.
-
-This file is part of Quake III Arena source code.
-
-Quake III Arena source code is free software; you can redistribute it
-and/or modify it under the terms of the GNU General Public License as
-published by the Free Software Foundation; either version 2 of the License,
-or (at your option) any later version.
-
-Quake III Arena source code is distributed in the hope that it will be
-useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
-MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-GNU General Public License for more details.
-
-You should have received a copy of the GNU General Public License
-along with Quake III Arena source code; if not, write to the Free Software
-Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
-===========================================================================
-*/
-//
-// math.s
-// x86 assembly-language math routines.
-
-#include "qasm.h"
-
-
-#if	id386
-
-	.text
-
-// TODO: rounding needed?
-// stack parameter offset
-#define	val	4
-
-.globl C(Invert24To16)
-C(Invert24To16):
-
-	movl	val(%esp),%ecx
-	movl	$0x100,%edx		// 0x10000000000 as dividend
-	cmpl	%edx,%ecx
-	jle		LOutOfRange
-
-	subl	%eax,%eax
-	divl	%ecx
-
-	ret
-
-LOutOfRange:
-	movl	$0xFFFFFFFF,%eax
-	ret
-
-#endif	// id386