genirq: Forgotten updates/deletions after removal of compat code

commit 0c6f8a8b917ad361319c8ace3e9f28e69bfdb4c1 ("genirq: Remove compat code")
removed the compat code, but forgot to update some references in comments and
delete some of its documentation.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: http://lkml.kernel.org/r/%3C1302426113-13808-1-git-send-email-geert%40linux-m68k.org%3E
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>