[lib] Remove KeyserverInfoPartial type

Summary:
Following the Flow upgrade, I'm looking at replacing all usages of $Shape in our codebase. Context here.

When I swapped the $Shape in KeyserverInfoPartial into a Partial, it revealed a type error. The issue is that the urlPrefix and connectionStatus we pass to createBoundServerCallsSelector are nullable, but that function requires them to be set.

I investigated further and found that we don't actually use KeyserverInfoPartial in any case where its "partialness" is necessary... it appears we just get the KeyserverInfos from the Redux store and pass them in. As such, I deleted the type and replaced usages with KeyserverInfos.

Depends on D10082

Test Plan: Flow

Reviewers: inka, michal

Reviewed By: inka

Subscribers: ginsu, tomek

Differential Revision: https://phab.comm.dev/D10083