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-plugin-transform-strict-mode/test/fixtures/auxiliary-comment/use-strict-add/expected.js

@@ -1,3 +1,5 @@
-/*before*/"use strict";
+/*before*/
+"use strict";
 
-/*after*/foo();
+/*after*/
+foo();

packages/babel-plugin-transform-strict-mode/test/fixtures/strict-mode/leading-comments/expected.js

@@ -1,5 +1,4 @@
 "use strict";
 
 // comments
-
-module.exports = {};
+module.exports = {};