alpha: cleanup: remove __NR_sys_epoll_*, leave __NR_epoll_*

__NR_sys_epoll_create and friends are alpha-specific
while __NR_epoll_create is a generic name for other
arches.

Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: linux-alpha@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
Signed-off-by: Matt Turner <mattst88@gmail.com>