More Cilk Plus removal

	contrib/
	* update-copyright.py: Remove "libcilkrts" reference.
	gcc/c-family/
	* c-attribs.c (c_common_attribute_table): Remove "cilk simd
	function".
	gcc/
	* doc/invoke.texi: Remove "Cilk Plus" references.

From-SVN: r258141