Drop SSPI auth support and more Windows files (#7148)

## Dropping SSPI auth support

SSPI authentication relied on Microsoft Windows support, removal started in https://codeberg.org/forgejo/forgejo/pulls/5353, because it was broken anyway. We have no knowledge of any users using SSPI authentication. However, if you somehow managed to run Forgejo on Windows, or want to upgrade from a Gitea version which does, please ensure that you do not use SSPI as an authentication mechanism for user accounts. Feel free to reach out if you need assistance.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/7148
Reviewed-by: Gusted <gusted@noreply.codeberg.org>
Reviewed-by: 0ko <0ko@noreply.codeberg.org>
Co-authored-by: Otto Richter <otto@codeberg.org>
Co-committed-by: Otto Richter <otto@codeberg.org>

modules/setting/path.go

@@ -34,11 +34,7 @@ var (
 func getAppPath() (string, error) {
 	var appPath string
 	var err error
-	if IsWindows && filepath.IsAbs(os.Args[0]) {
-		appPath = filepath.Clean(os.Args[0])
-	} else {
-		appPath, err = exec.LookPath(os.Args[0])
-	}
+	appPath, err = exec.LookPath(os.Args[0])
 	if err != nil {
 		if !errors.Is(err, exec.ErrDot) {
 			return "", err