Remove whitespace generation (#5833)

* Remove whitespace generation and rely on default printing

Changes to printing:
* Add newline after last empty SwitchCase
* Add newlines around block comments if they are non-flow comments or contain newlines

* Fix a few more fixtures

packages/babel-generator/test/fixtures/comments/variable-declarator-trailing-comment/expected.js

@@ -1,18 +1,20 @@
 {
-  var t = 20; /*
-               * This is trailing comment
-               */
+  var t = 20;
+  /*
+   * This is trailing comment
+   */
 }
-
 {
-  var tt = 20; /*
-                * This is trailing comment
-                */
+  var tt = 20;
+  /*
+   * This is trailing comment
+   */
 }
 {
   {
-    var t = 20; /*
-                 * This is trailing comment
-                 */
+    var t = 20;
+    /*
+     * This is trailing comment
+     */
   }
-}
+}