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-generator/test/fixtures/flow/interfaces-module-and-script/expected.js

@@ -1,9 +1,23 @@
-interface A {};
-interface A extends B {};
-interface A<T> extends B<T>, C<T> {};
-interface A { foo: () => number };
-interface Dictionary { length: number, [index: string]: string, };
+interface A {}
+;
+interface A extends B {}
+;
+interface A<T> extends B<T>, C<T> {}
+;
+interface A {
+  foo: () => number
+}
+;
+interface Dictionary {
+  length: number,
+  [index: string]: string,
+}
+;
+
 class Foo implements Bar {}
+
 class Foo extends Bar implements Bat, Man<number> {}
+
 class Foo extends class Bar implements Bat {} {}
-class Foo extends class Bar implements Bat {} implements Man {}
+
+class Foo extends class Bar implements Bat {} implements Man {}