[prefix] Remove unsupported .exe prefix

The unfinished .exe prefix was brought over from legacy Etherboot.
There has been no demand for .exe images so this patch removes the
prefix.

Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
Signed-off-by: Marty Connor <mdc@etherboot.org>

src/arch/i386/Makefile.pcbios

@@ -25,7 +25,6 @@ MEDIA		+= dsk
 MEDIA		+= nbi
 MEDIA		+= hd
 MEDIA		+= raw
-MEDIA		+= exe
 
 # Padding rules
 #

src/arch/i386/prefix/exeprefix.S

@@ -1,41 +0,0 @@
-/*
-	Prefix for .exe images
-	Doesn't work yet, even though it starts off the same as a .com
-	image as shown by DOS debug.
-*/
-
-	.text
-	.code16
-	.arch i386
-	.section	".prefix", "ax", @progbits
-
-_prefix:
-	.byte	'M', 'Z'
-	.short	_exe_size_tail			/* tail */
-	.short	_exe_size_pages			/* pages */
-	.short	0				/* relocations */
-	.short	2				/* header paras */
-	.short	_exe_bss_size			/* min */
-	.short	0xFFFF				/* max paras */
-	.short	_exe_ss_offset			/* SS */
-	.short	_stack_size			/* SP */
-	.short	0				/* checksum */
-	.short	0				/* IP */
-	.short	0				/* CS */
-	.short	0x1C				/* reloc offset */
-	.short	0				/* overlay number */
-	.short	0				/* fill */
-	.short	0				/* fill */
-
-	.section ".text16", "ax", @progbits
-prefix_exit:
-	movw	$0x4c00,%ax		/* return to DOS */
-	int	$0x21			/* reach this on Quit */
-prefix_exit_end:
-	.previous
-
-/* The body of etherboot is attached here at build time.
- * Force 16 byte alignment
- */
-	.align 16,0
-_body: