arch/x86/timestamp.inc: Remove unused file

This is a romcc compiled bootblock leftover.

Change-Id: I8d4f8bcdac7e15d60540157e9d2ac98603320977
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/55007
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/arch/x86/timestamp.inc

@@ -1,23 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-only */
-
-/*
- * Store the initial timestamp for booting in mmx registers. This works
- * because the bootblock isn't being compiled with MMX support so mm1 and
- * mm2 will be preserved into romstage.
- */
-	.code32
-
-.global stash_timestamp
-stash_timestamp:
-
-	/* Save the BIST value */
-	movl	%eax, %ebx
-
-	finit
-	rdtsc
-	movd	%ebx, %mm0
-	movd	%eax, %mm1
-	movd	%edx, %mm2
-
-	/* Restore the BIST value to %eax */
-	movl	%ebx, %eax