Update docs for `Button` to not consider `count` as required

[joshblack]

When visiting the documentation for Button, the count prop is marked as required. This is not the case for the component and the docs for Button should be updated to reflect that.

[siddharthkp]

That's odd! It's not required in the types.

Tracing back, looks like it was accidentally marked as required only for docs right around v36 (#2893). Safe to remove that required :)