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.

models/organization/team_test.go

@@ -8,6 +8,7 @@ import (
 
 	"code.gitea.io/gitea/models/db"
 	"code.gitea.io/gitea/models/organization"
+	repo_model "code.gitea.io/gitea/models/repo"
 	"code.gitea.io/gitea/models/unittest"
 
 	"github.com/stretchr/testify/assert"
@@ -42,9 +43,12 @@ func TestTeam_GetRepositories(t *testing.T) {
 
 	test := func(teamID int64) {
 		team := unittest.AssertExistsAndLoadBean(t, &organization.Team{ID: teamID})
-		assert.NoError(t, team.LoadRepositories(db.DefaultContext))
-		assert.Len(t, team.Repos, team.NumRepos)
-		for _, repo := range team.Repos {
+		repos, err := repo_model.GetTeamRepositories(db.DefaultContext, &repo_model.SearchTeamRepoOptions{
+			TeamID: team.ID,
+		})
+		assert.NoError(t, err)
+		assert.Len(t, repos, team.NumRepos)
+		for _, repo := range repos {
 			unittest.AssertExistsAndLoadBean(t, &organization.TeamRepo{TeamID: teamID, RepoID: repo.ID})
 		}
 	}