Don't dup after fetch_dimension_const

Any duplication that may be necessary must have happened earlier
already. Also I'm not sure what the IS_REF branch was there for
originally, but it does not appear to be relevant anymore.

Zend/zend_ast.c

@@ -452,16 +452,8 @@ ZEND_API int zend_ast_evaluate(zval *result, zend_ast *ast, zend_class_entry *sc
 				zval_dtor(&op1);
 				ret = FAILURE;
 			} else {
-				zval tmp;
+				zend_fetch_dimension_const(result, &op1, &op2, (ast->attr == ZEND_DIM_IS) ? BP_VAR_IS : BP_VAR_R);
 
-				zend_fetch_dimension_const(&tmp, &op1, &op2, (ast->attr == ZEND_DIM_IS) ? BP_VAR_IS : BP_VAR_R);
-
-				if (UNEXPECTED(Z_ISREF(tmp))) {
-					ZVAL_COPY_OR_DUP(result, Z_REFVAL(tmp));
-				} else {
-					ZVAL_COPY_OR_DUP(result, &tmp);
-				}
-				zval_ptr_dtor(&tmp);
 				zval_dtor(&op1);
 				zval_dtor(&op2);
 			}