[TESTS] Move CreateDeclarativeRepo to more accessible location

- This allows `CreateDeclarativeRepo` to be used by other testing
packages such as E2EE testing.
- Removes unused function in `services/webhook/sourcehut/builds_test.go`.

tests/integration/pull_create_test.go

@@ -126,7 +126,7 @@ func TestPullCreateWithPullTemplate(t *testing.T) {
 				}
 			}
 
-			repo, _, deferrer := CreateDeclarativeRepo(t, baseUser, "", nil, nil, changeOps)
+			repo, _, deferrer := tests.CreateDeclarativeRepo(t, baseUser, "", nil, nil, changeOps)
 
 			return repo, deferrer
 		}