Added release function to PoolVector::Access.

For clarity, assign-to-release idiom for PoolVector::Read/Write
replaced with a function call.
Existing uses replaced (or removed if already handled by scope)

core/variant.cpp

@@ -2418,9 +2418,6 @@ Variant::Variant(const PoolVector<Face3> &p_face_array) {
 			for (int j = 0; j < 3; j++)
 				w[i * 3 + j] = r[i].vertex[j];
 		}
-
-		r = PoolVector<Face3>::Read();
-		w = PoolVector<Vector3>::Write();
 	}
 
 	type = NIL;