Replace custom Go formatter with golangci-lint fmt (#37194)

Use `golangci-lint fmt` to format code, replacing the previous custom
formatter tool. https://github.com/daixiang0/gci is used to order the
imports.

`make fmt` performs ~13% faster while consuming ~57% less cpu while
formatting for me.

`GOFUMPT_PACKAGE` is gone because it's using the builtin package from
golangci-lint.

Co-authored-by: Claude (claude-opus-4-6) <noreply@anthropic.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

services/user/delete.go

@@ -8,8 +8,6 @@ import (
 	"fmt"
 	"time"
 
-	_ "image/jpeg" // Needed for jpeg support
-
 	actions_model "code.gitea.io/gitea/models/actions"
 	activities_model "code.gitea.io/gitea/models/activities"
 	asymkey_model "code.gitea.io/gitea/models/asymkey"
@@ -24,6 +22,8 @@ import (
 	user_model "code.gitea.io/gitea/models/user"
 	"code.gitea.io/gitea/modules/setting"
 
+	_ "image/jpeg" // Needed for jpeg support
+
 	"xorm.io/builder"
 )