Refactor deletion (#28610)

Introduce the new generic deletion methods
- `func DeleteByID[T any](ctx context.Context, id int64) (int64, error)`
- `func DeleteByIDs[T any](ctx context.Context, ids ...int64) error`
- `func Delete[T any](ctx context.Context, opts FindOptions) (int64,
error)`

So, we no longer need any specific deletion method and can just use
the generic ones instead.

Replacement of #28450

Closes #28450

---------

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

routers/web/admin/notice.go

@@ -8,6 +8,7 @@ import (
 	"net/http"
 	"strconv"
 
+	"code.gitea.io/gitea/models/db"
 	system_model "code.gitea.io/gitea/models/system"
 	"code.gitea.io/gitea/modules/base"
 	"code.gitea.io/gitea/modules/context"
@@ -55,7 +56,7 @@ func DeleteNotices(ctx *context.Context) {
 		}
 	}
 
-	if err := system_model.DeleteNoticesByIDs(ctx, ids); err != nil {
+	if err := db.DeleteByIDs[system_model.Notice](ctx, ids...); err != nil {
 		ctx.Flash.Error("DeleteNoticesByIDs: " + err.Error())
 		ctx.Status(http.StatusInternalServerError)
 	} else {

routers/web/repo/setting/setting.go

@@ -418,7 +418,7 @@ func SettingsPost(ctx *context.Context) {
 			Interval:      interval,
 			RemoteAddress: remoteAddress,
 		}
-		if err := repo_model.InsertPushMirror(ctx, m); err != nil {
+		if err := db.Insert(ctx, m); err != nil {
 			ctx.ServerError("InsertPushMirror", err)
 			return
 		}