[vector] Add std::move to pop()

This was removed in 76fc27713f,
but I believe that was faultly. It was because of a bad move
implementation in the set.

src/hb-vector.hh

@@ -364,7 +364,7 @@ struct hb_vector_t
   Type pop ()
   {
     if (!length) return Null (Type);
-    Type v = arrayZ[length - 1];
+    Type v {std::move (arrayZ[length - 1])};
     arrayZ[length - 1].~Type ();
     length--;
     return v;