x86: remove misleading comments in trampoline_*.S

Both trampolines actually *do* set up stack. (Is the "we jump into
compressed/head.S" comment still true?)

Signed-off-by: Pavel Machek <pavel@suse.cz>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>