Clear renderCalendarInfo timeout before assigning a new timeout (#1323)

[mackinleysmith]

This is a do-over of @mstanaland's work on #1736 to fix a memory leak issue where the timeout is not cleared before being set again. I am doing this so that we can be current with master, since the original PR went unmerged for six months due to lack of a unit test. This branch does contain a test displaying that setState is called by the timeout only once.

Original PR description by @mstanaland:

Clears the setTimeout assigned to this.setCalendarInfoWidthTimeout before a new setTimeout is assigned/reassigned to prevent a possible memory leak.
Fixes issue #1323

[mackinleysmith]

Looks like the failures in Travis CI are not related to the code changed by this PR. @ljharb is this normal for this project?

EDIT: it looks like I was wrong, one of the failures is from my new test.
https://travis-ci.org/github/airbnb/react-dates/jobs/708032208#L1363

The error I'm getting (only in CI, it works for me locally) is can't redefine non-configurable property "window", which I got by calling this from mocha-wrap:

wrap().withGlobal('window', () => ({ getComputedStyle: sinon.stub().returns({}) }))

@ljharb it would be great to get your input on how to properly do this. I'm feeling a little stumped as to how to write a good test for this situation.

[ljharb]

In the future, please do not create a second, duplicate PR - post a link to your branch and I can update the original PR. Now both of these need to stay open and kept in sync for the duration.

[ljharb]

If that's the only failure, it's something I can try to look into in the next week or so.

[mackinleysmith]

Okay sure, would you like me to close this PR?

[ljharb]

@smit1625 no, please don't close it :-) i'll need to keep it in sync with #1736 until both are landed.