lib/util: remove extra safe_string.h file

lib/util: remove extra safe_string.h file

lib/util/safe_string.h is similar to source3/include/safe_string.h, but
the former has fewer checks. It is missing bcopy, strcasecmp, and
strncasecmp.

Add the missing elements to lib/util/safe_string.h remove the other
safe_string.h which is in the source3-specific path. To accomodate
existing uses of str(n?)casecmp, add #undef lines to source files where
they are used.

Signed-off-by: Matthew DeVore <matvore@google.com>
Reviewed-by: David Mulder <dmulder@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Fri Aug 28 02:18:40 UTC 2020 on sn-devel-184