Remove fallbacks for strtoll, strtoull.

Remove fallbacks for strtoll, strtoull.

strtoll was backfilled with either __strtoll or strtoq on systems without
strtoll. The last such system on the buildfarm was an ancient HP-UX animal. We
don't support HP-UX anymore, so remove.

On other systems strtoll was present, but did not have a declaration. The last
known instance on the buildfarm was running an ancient OSX and shut down in
2019.

Author: Andres Freund <andres@anarazel.de>
Reviewed-by: Thomas Munro <thomas.munro@gmail.com>
Discussion: https://postgr.es/m/20220804013546.h65najrzig764jar@awork3.anarazel.de