This patch removes some stray (unused) *_internal aliases, and
function prototypes with no corresponding definitions at all, at least
some of which were missed in previous INTDEF / INTUSE removal.
Not removed in this patch: __canonicalize_directory_name_internal,
noticed in the course of preparing this patch, isn't an alias, but an
actual function in sysdeps/mach/hurd/getcwd.c - apparently unused,
however.
Tested for x86_64 that installed stripped shared libraries are
unchanged by this patch.