remove transformer prepass and various other optimisations

test/core/fixtures/transformation/es7.exponentian-operator/assignment/actual.js

@@ -1,2 +1,3 @@
+var num = 1;
 num **= 2;
 ;

test/core/fixtures/transformation/es7.exponentian-operator/assignment/expected.js

@@ -1,5 +1,6 @@
 "use strict";
 
+var num = 1;
 num = Math.pow(num, 2);
 
 ;

test/core/fixtures/transformation/spec.function-name/assignment/actual.js

@@ -4,4 +4,5 @@ var i = function () {
 
 var j = function () {
   ({ j } = 5);
+  ;
 };

test/core/fixtures/transformation/spec.function-name/assignment/expected.js

@@ -17,4 +17,6 @@ var i = (function (_i) {
 var j = function j() {
   var _ = 5;
   j = _.j;
+
+  ;
 };