Better Query on repo.index

## Description and Impact
Changes how repo.index queries for things

## Deploy Plan
> Does Infrastructure need to know anything special about this deploy?

## Rollback Plan
* To roll back this change, revert the merge with: `git revert -m 1 MERGE_SHA` and perform another deploy.

## URLs
> Links to bug tickets or user stories.

## QA Plan
> Fill in scenarios below. Review [QA Best Practices](https://source.sportngin.com/page/show/1227795-qa-best-practices).

#### Risk Level:
- [X] Low
- [ ] Medium
- [ ] High

Rake app:hubstats:setup to build
Checkout that the number of comments and pulls in the active users table add up to the numbers displayed above
You already have a scope that does this: `User.belonging_to_repo`

You're also never using this anywhere.

Generally, with scopes, you want to keep scopes on the classes that you're that you're selecting from. In this case you're finding users, so the scope should be on `User`.