Bug on endpoint IsFollowingPublicKey

I was using this endpoint on an app and noticed a bug. It doesn't give the correct result if the user unfollowed the other user at some point.

## How to reproduce
- choose a user A that never followed user B
- test the endpoint. It will return the correct value (false)
- make the user A follow user B. It will return the correct value (true)
- make the user A unfollow user B. It will always return `true` from now on.

@mubashariqbal are you still actively using this endpoint?

Start by locating the IsFollowingPublicKey HTTP endpoint and reproduce the sequence in the issue: never followed, followed, then unfollowed. Done means the endpoint returns false after the unfollow, while preserving the correct false and true results for the earlier states.

Written by the indexing model from the issue text.