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-object-rest-spread/test/fixtures/object-spread/expression/expected.js

@@ -1,3 +1,9 @@
 var _extends = Object.assign || function (target) { for (var i = 1; i < arguments.length; i++) { var source = arguments[i]; for (var key in source) { if (Object.prototype.hasOwnProperty.call(source, key)) { target[key] = source[key]; } } } return target; };
 
-_extends({ x }, y, { a }, b, { c });
+_extends({
+  x
+}, y, {
+  a
+}, b, {
+  c
+});