Remove Promise#finally from course search

[hawkrives]

Closes #2502

There are two changes in here.

---

	componentDidMount() {
-		areAnyTermsCached().then(anyTermsCached => {
-			if (anyTermsCached) {
-				this.loadData()
-			} else {
-				this.setState(() => ({dataLoading: false}))
-			}
-		})
+		this.loadData()

This one … so far as I can tell, the check here is duplicated in loadData, both in the if (this.props.courseDataState !== 'ready') check and the if (await areAnyTermsCached()).

That is to say, we need to call loadData if the courses haven't been loaded into RAM (courseDataState !== 'ready'), and … well, TBH I can't quite tell why the areAnyTermsCached was there in componentDidMount.

---

The other change is to remove the .finally(() => this.doneLoading()) line from loadData. I did this by converting it from a promise chain to an async function. My translation should be equivalent here, esp. the this.setState(() => ({dataLoading: false})) bit right after the if-else blocks.