Consolidate Linux epoll_wait syscall

This patch consolidates the epoll_wait Linux syscall generation on
sysdeps/unix/sysv/linux/epoll_wait.c.  The implementation tries to
use __NR_epoll_wait if defined, otherwise calls epoll_pwait.

Checked on i686-linux-gnu, x86_64-linux-gnu, x86_64-linux-gnux32,
arch64-linux-gnu, arm-linux-gnueabihf, and powerpc64le-linux-gnu.

	* sysdeps/unix/sysv/linux/epoll_wait.c: New file.
	* sysdeps/unix/sysv/linux/generic/epoll_wait.c: Remove file.
	* sysdeps/unix/sysv/linux/syscalls.list: Remove epoll_wait from
	auto-generation list.