[x86 setup] build/tools.c: fix comment

Correct a comment in arch/i386/boot/build/tools.c; we now build the
kernel from only two components instead of three, since the boot
sector has been integrated in the setup code.
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

arch/i386/boot/tools/build.c

@@ -5,7 +5,7 @@
  */
 
 /*
- * This file builds a disk-image from three different files:
+ * This file builds a disk-image from two different files:
  *
  * - setup: 8086 machine code, sets up system parm
  * - system: 80386 code for actual system