posix: Consolidate Linux waitpid syscall

posix: Consolidate Linux waitpid syscall

This patch consolidates the waitpid Linux syscall generation on
sysdeps/unix/sysv/linux/waitpid.c.  It basically removes it from
architecture auto-generation list and also remove arch specific
implementations.

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/sh/syscalls.list: Remove waitpid from
	auto-generated list.
	* sysdeps/unix/sysv/linux/m68k/syscalls.list: Likewise.
	* sysdeps/unix/sysv/linux/i386/syscalls.list: Likewise.
	* sysdeps/unix/sysv/linux/sparc/syscalls.list: Remove file.
	* sysdeps/unix/sysv/linux/tile/waitpid.S: Likewise.
	* sysdeps/unix/sysv/linux/powerpc/syscalls.list: Likewise.