avm1: Remove unnecessary MovieClip coercions

[turicfr]

Previously, removed MovieClips that were passed to a function using one of CallFunction/CallMethod/NewObject/NewMethod were coerced to a boxed undefined object. Here's an example:

var mc = this.createEmptyMovieClip("mc", 1);
removeMovieClip(mc);

// CallFunction
f(mc);

// CallMethod
_root.f(mc);

// NewObject
new f(mc);

// NewMethod
new _root.f(mc);

function f(a) {
    trace(a == undefined); // false in Flash, true in Ruffle
    trace(typeof a); // movieclip in Flash, object in Ruffle
}

Fixes #15265.