more add_target removals

more add_target removals

This removes a few more erroneous calls to add_target.  These calls
end up installing the target in a user-visible way; but these targets
are all auto-activated and, I think, should never be explicitly
requested.

I have no way to test these.

	* aix-thread.c (_initialize_aix_thread): Use
	complete_target_initialization.
	* bsd-uthread.c (_initialize_bsd_uthread): Use
	complete_target_initialization.
	* dec-thread.c (_initialize_dec_thread): Use
	complete_target_initialization.
	* ravenscar-thread.c (_initialize_ravenscar): Use
	complete_target_initialization.
	* sol-thread.c (_initialize_sol_thread): Use
	complete_target_initialization.
	* spu-multiarch.c (_initialize_spu_multiarch): Use
	complete_target_initialization.