Eliminate the Parameter type completely - now ParameterList is just

an overblown array of ParamDecl*'s that also keeps track of parenlocs
and has helper methods.

lib/SILGen/SILGenConstructor.cpp

@@ -91,7 +91,7 @@ static void emitImplicitValueConstructor(SILGenFunction &gen,
 
     elements.push_back(
       emitImplicitValueConstructorArg(gen, Loc,
-                                      param.decl->getType()->getCanonicalType(),
+                                      param->getType()->getCanonicalType(),
                                       ctor));
   }