Rewrite get using nvGet()

Profile data shows much heavier use of ArrayData::nvGet(),
nvGetCell(), and exists(), than get().  So rewrite get()
using nvGet().

hphp/runtime/base/array/policy_array.cpp

@@ -361,16 +361,6 @@ TypedValue* PolicyArray::nvGetCellImpl(K k) const {
 //   return toInt64(find(k, m_size));
 // }
 
-template <class K>
-const Variant& PolicyArray::getImpl(K k, bool error) const {
-  APILOG << "(" << keystr(k) << ", " << error << ")";
-  auto const pos = find(k, m_size);
-  if (pos != PosType::invalid) {
-    return val(pos);
-  }
-  return error ? getNotFound(k) : null_variant;
-}
-
 template <class K>
 ArrayData *PolicyArray::lvalImpl(K k, Variant*& ret,
                                   bool copy, bool checkExist) {