about RemoveHandler again

hi @kataras , another question here !

this case can remove handler successful
```golang
func Route(r router.Party) {
r.Use(middleware.Foo)
r.Get("/foo", ctrl.Index).RemoveHandler(middleware.Foo)
}
```

but this case failed
```golang
func Route(r *iris.APIContainer) {
sub := r.Party("/sub-r")
sub.Use(middleware.Foo)
sub.Get("/foo", ctrl.Index).RemoveHandler(middleware.Foo)
}
```

the difference is `r router.Party` and `r *iris.APIContainer`


and i find that `middleware.Foo` do not in `r.Handlers`

actually the handler that use in `app.UseGlobal(...)` can find in this `r.Handlers` ,

It bothers me a lot, and i think it is a `bug`, all the `handlers` shoud be added to `[]Handler`

_Originally posted by @sado0823 in https://github.com/kataras/iris/issues/1713#issuecomment-786394147_

Start by reproducing the two routing examples in the issue and compare the handlers returned by r.Handlers for router.Party versus *iris.APIContainer. Trace RemoveHandler and app.UseGlobal behavior from those entry points; done means middleware.Foo can be found and removed consistently in both cases, with regression coverage for each example.

Written by the indexing model from the issue text.