Remove unnecassary calls to filepath.Join (#17608)

- Partialy resolvess #17596
- Resolves `badCall` errors from go-critic `badCall: suspicious Join on
1 argument`
- When only 1 argument is passed into `filepath.Join`, it won't do
anything special other than `filepath.Clean(...)` will be applied over
it.

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: 6543 <6543@obermui.de>

routers/web/user/setting/adopt.go

@@ -27,7 +27,7 @@ func AdoptOrDeleteRepository(ctx *context.Context) {
 	action := ctx.FormString("action")
 
 	ctxUser := ctx.User
-	root := filepath.Join(models.UserPath(ctxUser.LowerName))
+	root := models.UserPath(ctxUser.LowerName)
 
 	// check not a repo
 	has, err := models.IsRepositoryExist(ctxUser, dir)