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/user/user_test.go

@@ -5,7 +5,6 @@ package user
 
 import (
 	"os/exec"
-	"runtime"
 	"strings"
 	"testing"
 )
@@ -23,10 +22,6 @@ func TestCurrentUsername(t *testing.T) {
 	if len(user) == 0 {
 		t.Errorf("expected non-empty user, got: %s", user)
 	}
-	// Windows whoami is weird, so just skip remaining tests
-	if runtime.GOOS == "windows" {
-		t.Skip("skipped test because of weird whoami on Windows")
-	}
 	whoami, err := getWhoamiOutput()
 	if err != nil {
 		t.Errorf("failed to run whoami to test current user: %f", err)