Clear tableTypes collection when TablePage unmounts to avoid memory leak

[Arooba-git]

Hello 👋
As part of our project, we are using Facebook's new Memlab tool to detect memory leaks in SPA applications.
While running the tool and analyzing the code of react-reduction, we saw that your project does a very good job of ensuring that all async operations are cancelled when the component unmounts. However, as per Memlab execution results, we found a dangling collection that was causing the memory to leak (screenshots below).

[before]

Hence we added the fix by clearing the collection on unmount, and you can see the heap size and # of leaks reducing noticeably:

Note: We used splice instead of the more conventional .length=0, to cater for any future modifications where tableTypes may have a length property but is not assignable.

You can analyze this and other potential leak sources, if you like, by running Memlab with a scenario file covering the maximum # of use cases.
Following is a sample of the scenario file we used (it needs to be a .js file but attaching here in .txt form):

react-reduction-memlab-scenario.txt

Note that some other reported leaks (in Memlab) originated from React's internal objects, and hence were ignored.