Fix submit button won't refresh in New Repository Fork page (#22994)

Fork a repo, and input an invalid repo name, you will get an error.
Then rename the repo name to a valid one, the submit button is still
disabled.

In other pages, for example, in create repo page, the submit button will
not be disabled.
So I removed the codes to disable the submit button.

routers/web/repo/pull.go

@@ -203,6 +203,7 @@ func Fork(ctx *context.Context) {
 func ForkPost(ctx *context.Context) {
 	form := web.GetForm(ctx).(*forms.CreateRepoForm)
 	ctx.Data["Title"] = ctx.Tr("new_fork")
+	ctx.Data["CanForkRepo"] = true
 
 	ctxUser := checkContextUser(ctx, form.UID)
 	if ctx.Written() {