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-do-expressions/test/fixtures/do-expressions/block-scope/expected.js

@@ -1,5 +1,4 @@
 var _a;
 
 var a = 1;
-
-_a = 2, _a;
+_a = 2, _a;

packages/babel-plugin-transform-do-expressions/test/fixtures/do-expressions/while-if/expected.js

@@ -1,4 +1,5 @@
 let p;
+
 let a = function () {
   var _ret;
 
@@ -9,5 +10,6 @@ let a = function () {
       _ret = 'b';
     }
   }
+
   return _ret;
-}();
+}();