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-runtime/test/fixtures/runtime/aliased-constructors/expected.js

@@ -5,6 +5,7 @@ obj.constructor === Object;
 obj.constructor === _Promise;
 
 _Symbol();
+
 _Symbol("test");
 
-new _Map();
+new _Map();