[iter] Remove passing pointer to hb_iter()

While doable with hb_deref_pointer() as well, we also would then
need to do it in a ton of places.  Not worth it / messy.
diff --git a/src/hb-array.hh b/src/hb-array.hh
index fc8d39d..4e8933f 100644
--- a/src/hb-array.hh
+++ b/src/hb-array.hh
@@ -279,7 +279,7 @@
 uint32_t hb_array_t<T>::hash () const
 {
   return
-  + hb_iter (this)
+  + hb_iter (*this)
   | hb_map (hb_hash)
   | hb_reduce ([] (uint32_t a, uint32_t b) -> uint32_t { return a * 31 + b; }, 0)
   ;