remove es20xx prefixes from plugins and rename folders (#6575)

packages/babel-plugin-transform-classes/test/fixtures/spec/instance-method/actual.js

@@ -0,0 +1,5 @@
+class Test {
+  test() {
+  return 5 + 5;
+  }
+}

packages/babel-plugin-transform-classes/test/fixtures/spec/instance-method/expected.js

@@ -0,0 +1,15 @@
+var Test =
+/*#__PURE__*/
+function () {
+  function Test() {
+    babelHelpers.classCallCheck(this, Test);
+  }
+
+  babelHelpers.createClass(Test, [{
+    key: "test",
+    value: function test() {
+      return 5 + 5;
+    }
+  }]);
+  return Test;
+}();