Figure out if we need `polyfills.ts`

We get this warning: 
```
Warning: /Users/lamberty/Documents/3601/iteration-1-blueberries/client/src/polyfills.ts is part of the TypeScript compilation but it's unused.
Add only entry points to the 'files' or 'include' properties in your tsconfig.
```
and I'm not sure if we can remove `polyfills.ts` or not.

