Bug 1658432: Don't remove wrapping CALayer from its superview outside of...

Bug 1658432: Don't remove wrapping CALayer from its superview outside of Commit. r=mac-reviewers,mstange, a=dsmith

This change lets NativeLayerRootCA::Representation::Commit be the only
point where sublayers are added and removed from the root CALayer.

Differential Revision: https://phabricator.services.mozilla.com/D191673