Fix js warnings (#2693)

* react: using prop-types package to fix deprecated React.PropTypes property warning

https://facebook.github.io/react/warnings/dont-call-proptypes.html

* removing babel devDependency because has been deprecated in favor of babel-cli

this fixes a warning during `npm install`:
```
npm WARN deprecated babel@6.23.0:
In 6.x, the babel package has been deprecated in favor of babel-cli.
Check https://opencollective.com/babel to support the Babel maintainers
```

* js: setting ExploreActionButtons.queryEndpoint PropType as required

because it's required in the child component DisplayQueryButton

* js(tests): using object in expandedSlices prop type of SliceCell tests

* js(tests): adding required props to SqlEditor mockedProps

* js(tests): adding required prop editorHeight to TabbedSqlEditors mockedProps

* js: removing unused moments dependency

superset/assets/javascripts/explorev2/components/ExploreActionButtons.jsx

@@ -8,7 +8,7 @@ import DisplayQueryButton from './DisplayQueryButton';
 const propTypes = {
   canDownload: PropTypes.oneOfType([PropTypes.string, PropTypes.bool]).isRequired,
   slice: PropTypes.object,
-  queryEndpoint: PropTypes.string,
+  queryEndpoint: PropTypes.string.isRequired,
   queryResponse: PropTypes.object,
   chartStatus: PropTypes.string,
 };