d: Remove Wtemplates warnings from the code generation pass

These have been superceded by the front-end's own internal tracking of
instantiations, exposed by `-ftransition=templates'.

gcc/d/ChangeLog:

	* d-lang.cc: Include dmd/template.h.
	(d_parse_file): Call printTemplateStats when vtemplates is set.
	* decl.cc (start_function): Remove OPT_Wtemplates warning.
	* lang.opt (Wtemplates): Remove.