spec/function.dd: Remove "ref" from "return ref"

Return-ref parameters don't need to specifically be declared with the
exact token sequence "return ref". For example, "ref return" also
works, as does e.g. "return scope int* a".

Author: CyberShadow

spec/function.dd

@@ -56,7 +56,7 @@ $(GNAME InOut):
     $(D lazy)
     $(D out)
     $(D ref)
-    $(RELATIVE_LINK2 return-ref-parameters, $(D return ref))
+    $(RELATIVE_LINK2 return-ref-parameters, $(D return))
     $(D scope)
 
 $(GNAME VariadicArgumentsAttributes):