libctf, include: remove the nondeduplicating CTF linker

The nondeduplicating CTF linker was kept around when the deduplicating
one was added so that people had something to fall back to in case the
deduplicating linker turned out to be buggy.  It's now much more stable
than the nondeduplicating linker, in addition to much faster, using much
less memory and producing much better output.  In addition, while
libctf has a linker flag to invoke the nondeduplicating linker, ld does
not expose it: the only way to turn it on within ld is an intentionally-
undocumented environment variable.  So we can remove it without any ABI
or user-visibility concerns (the only thing we leave around is the
CTF_LINK_NONDEDUP flag, which can easily be interpreted as "deduplicate
less", though right now it does nothing).

This lets us remove a lot of complexity associated with tracking
filenames and CU names separately (something the deduplcating linker
never bothered with, since the cunames are always reliable and ld never
hands us useful filenames anyway)

The biggest lacuna left behind is the ctf_type_mapping machinery, which
slows down deduplicating links quite a lot.  We can't just ditch it
because ctf_add_type uses it: removing the slowdown from the
deduplicating linker is a job for another commit.

include/ChangeLog
2021-03-02  Nick Alcock  <nick.alcock@oracle.com>

	* ctf-api.h (CTF_LINK_SHARE_DUPLICATED): Note that this might
	merely change how much deduplication is done.

libctf/ChangeLog
2021-03-02  Nick Alcock  <nick.alcock@oracle.com>

	* ctf-link.c (ctf_create_per_cu): Drop FILENAME now that it is
	always identical to CUNAME.
	(ctf_link_deduplicating_one_symtypetab): Adjust.
	(ctf_link_one_type): Remove.
	(ctf_link_one_input_archive_member): Likewise.
	(ctf_link_close_one_input_archive): Likewise.
	(ctf_link_one_input_archive): Likewise.
	(ctf_link): No longer call it.  Drop CTF_LINK_NONDEDUP path.
	Improve header comment a bit (dicts, not files).  Adjust
	ctf_create_per_cu call.
	(ctf_link_deduplicating_variables): Simplify.
	(ctf_link_in_member_cb_arg_t) <cu_name>: Remove.
	<in_input_cu_file>: Likewise.
	<in_fp_parent>: Likewise.
	<done_parent>: Likewise.
	(ctf_link_one_variable): Turn uses of in_file_name to in_cuname.

include/ctf-api.h

@@ -94,7 +94,8 @@ typedef struct ctf_link_sym
 /* Share only types that are used by multiple inputs.  */
 #define CTF_LINK_SHARE_DUPLICATED 0x1
 
-/* Do a nondeduplicating link.  */
+/* Do a nondeduplicating link, or otherwise deduplicate "less hard", trading off
+   CTF output size for link time.  */
 #define CTF_LINK_NONDEDUP 0x2
 
 /* Create empty outputs for all registered CU mappings even if no types are