Move RepoTransfer from models to models/repo sub package (#32506)

`RepoTransfer` now is at models, but if we want to move it into `repo`
model, it will depend on `Team`. So this PR also makes repo model depend
on org model to make it possible. Just refactor, no code change.

- [x] Move `DeleteOrganization` from `models/organization` to service
layer
- [x] Move `AccessibleTeamReposEnv` to `models/repo`
- [x] Move `RepoTransfer` from `models` to `models/repo`
- [x] Merge `getUserTeamIDs` and `GetUserTeamIDs`, Merge `GetUserTeams`
and `getUserTeams`.
- [x] Remove `Team`'s `Repos []*repo_model.Repository` to avoid dependency recycle.

services/org/user.go

@@ -60,7 +60,7 @@ func RemoveOrgUser(ctx context.Context, org *organization.Organization, user *us
 	}
 
 	// Delete all repository accesses and unwatch them.
-	env, err := organization.AccessibleReposEnv(ctx, org, user.ID)
+	env, err := repo_model.AccessibleReposEnv(ctx, org, user.ID)
 	if err != nil {
 		return fmt.Errorf("AccessibleReposEnv: %w", err)
 	}