refactor: git repo and relative path handling (#38522)

1. simplify "StorageRepo" code
2. simplify git.OpenRepository code
3. by the way, clean up some unused files in git test fixtures.

models/repo/repo_location_test.go

@@ -0,0 +1,27 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package repo_test
+
+import (
+	"testing"
+
+	repo_model "gitea.dev/models/repo"
+	"gitea.dev/models/unittest"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestRepository_GitRepo(t *testing.T) {
+	assert.NoError(t, unittest.PrepareTestDatabase())
+
+	repo := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{ID: 1})
+
+	assert.Equal(t, "user2/repo1.git", repo_model.CodeRepoByName(repo.OwnerName, repo.Name).GitRepoLocation())
+	assert.Equal(t, "user2/repo1.git", repo.CodeStorageRepo().GitRepoLocation())
+	assert.Equal(t, "repo-1", repo.CodeStorageRepo().GitRepoManagedID())
+
+	assert.Equal(t, "user2/repo1.wiki.git", repo_model.WikiRepoByName(repo.OwnerName, repo.Name).GitRepoLocation())
+	assert.Equal(t, "user2/repo1.wiki.git", repo.WikiStorageRepo().GitRepoLocation())
+	assert.Equal(t, "repo-wiki-1", repo.WikiStorageRepo().GitRepoManagedID())
+}