Remove TimerMixin from TouchableWithoutFeedback (#21493)

Summary:
Related to #21485.
Removed `TimerMixin` from the `TouchableWithoutFeedback` component since it is currently not used.
Added tests cases for `TouchableWithoutFeedback` to check for any runtime issues.
Pull Request resolved: https://github.com/facebook/react-native/pull/21493

Differential Revision: D10219098

Pulled By: RSNara

fbshipit-source-id: d9517b2bd5b72b0450fa864f3556673ae3181552

Libraries/Components/Touchable/TouchableWithoutFeedback.js

@@ -13,7 +13,6 @@
 const DeprecatedEdgeInsetsPropType = require('DeprecatedEdgeInsetsPropType');
 const React = require('React');
 const PropTypes = require('prop-types');
-const TimerMixin = require('react-timer-mixin');
 const Touchable = require('Touchable');
 const View = require('View');
 
@@ -80,7 +79,7 @@ export type Props = $ReadOnly<{|
  */
 const TouchableWithoutFeedback = ((createReactClass({
   displayName: 'TouchableWithoutFeedback',
-  mixins: [TimerMixin, Touchable.Mixin],
+  mixins: [Touchable.Mixin],
 
   propTypes: {
     accessible: PropTypes.bool,