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-react-constant-elements/test/fixtures/constant-elements/pure-deopt/expected.js

@@ -1,5 +1,7 @@
 // https://github.com/facebook/react/issues/3226
 // Not safe to reuse because it is mutable
 function render() {
-  return <div style={{ width: 100 }} />;
-}
+  return <div style={{
+    width: 100
+  }} />;
+}