libctf: create: non-root-visible types should not appear in name tables

We were accidentally interning newly-added and newly-opened
non-root-visible types into name tables, and removing names from name
tables when such types were removed.  This is very wrong: the whole
point of non-root-visible types is they do not go in name tables and
cannot be looked up by name.  This bug made non-root-visible types
basically identical to root-visible types, right back to the earliest
days of libctf in the Solaris era.

libctf/
	* ctf-open.c (init_types): Only intern root-visible types.
	* ctf-create.c (ctf_dtd_insert): Likewise.
	(ctf_dtd_delete): Only remove root-visible types.
	(ctf_rollback): Likewise.
	(ctf_add_generic): Adjust.
	(ctf_add_struct_sized): Adjust comment.
	(ctf_add_union_sized): Likewise.
	(ctf_add_enum): Likewise.
	* ctf-impl.h (ctf_dtd_insert): Adjust prototype.