clockevents: remove sysdev.h

This isn't needed in the clockevents.c file, and the header file is
going away soon, so just remove the #include

Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>