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-es2015-destructuring/test/fixtures/destructuring/array/expected.js

@@ -6,5 +6,4 @@ a = "hello";
 var _ref2 = [", ", "junk"];
 b = _ref2[0];
 c = "world";
-
-;
+;