Clean up Makefile, tests and legacy code (#36638)

This simplifies the Makefile by removing the whole-file wrapping that
creates a tempdir introduced by
https://github.com/go-gitea/gitea/pull/11126. REPO_TEST_DIR is removed
as well.

Also clean up a lot of legacy code: unnecessary XSS test, incorrect test
env init, unused "_old_uid" hack, etc

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

tests/test_utils.go

@@ -24,11 +24,8 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
-func InitTest(requireGitea bool) {
+func InitTest() {
 	testlogger.Init()
-
-	setting.SetupGiteaTestEnv()
-
 	unittest.InitSettingsForTesting()
 	setting.Repository.DefaultBranch = "master" // many test code still assume that default branch is called "master"
 
@@ -38,7 +35,7 @@ func InitTest(requireGitea bool) {
 
 	setting.LoadDBSetting()
 	if err := storage.Init(); err != nil {
-		testlogger.Fatalf("Init storage failed: %v\n", err)
+		testlogger.Panicf("Init storage failed: %v\n", err)
 	}
 
 	switch {