Stop generating <sys/linux-syscalls.h>.

The <asm/unistd.h> files contain the canonical data, and
<sys/glibc-syscalls.h> contain new glibc-compatible names,
and if you #include the standard <sys/syscall.h> you get
both sets of names.

Change-Id: I9919c080931c0ba1660f5e37c6a6265ea716d603