Mark various removed system calls as OBSOL instead of UNIMPL.

[jhb]

Summary

This is mostly a cosmetic change except that obsolete system calls are
assigned meaningful names in the names arrays which means that using
tools like kdump or truss against binaries invoking these system calls
will print out the name instead of the number. The script I use to
generate the XML list of syscalls for GDB also ignore UNIMPL but not
OBSOL entries. In general UNIMPL should only be used to reserve
placeholders for system calls that have never been implemented while
system calls that existed at one time in FreeBSD but were removed
should be marked OBSOL instead.

I noticed this when I was going to update the XML syscall list for GDB
for 12.0 and noticed it would remove the numa_* syscalls added in 11
which isn't quite friendly since GDB can be used on 11 still.

[kib]

Are the real changes only in syscall.masters ? The syscall.master' diffs look fine.

[imp]

This looks great to me. A tiny bit more memory usage for the strings, but that's small potatoes.

[jhb]

In D17344#369936, @kib wrote:

Are the real changes only in syscall.masters ? The syscall.master' diffs look fine.

The real changes are only there, but I did include the generated diff as well. Most of the generated changes are to comments except for freebsd32_syscalls.c and syscalls.c where some of the string constants change.