removeInertRoot(inertRoot) {
    this._throwIfDestroyed();
    this._inertRoots.delete(inertRoot);
    if (this._inertRoots.size === 0)
      this.destructor();
  }
Remove the given inert root from this inert node's set of managing inert roots.
If the set of managing inert roots becomes empty, this node is no longer inert,
so the object should be destroyed.
@param {InertRoot} inertRoot