[AppBar] Removed reference to deleted MDCAppBarParenting.
[AppBar] Removed reference to deleted MDCAppBarParenting.

Reviewers: O1 Material components iOS!, yiranm

Reviewed By: yiranm

Tags: #material_components_ios

Differential Revision: http://codereview.cc/D1575

samnm/material-components-ios,material-components/material-components-ios,Eccelor/material-components-ios,chriscox/material-components-ios,material-components/material-components-ios,Eccelor/material-components-ios,chriscox/material-components-ios,brianjmoore/material-components-ios,willlarche/material-components-ios,material-components/material-components-ios,willlarche/material-components-ios,samnm/material-components-ios,randallli/material-components-ios,randallli/material-components-ios,randallli/material-components-ios,sigito/material-components-ios,willlarche/material-components-ios,sigito/material-components-ios,brianjmoore/material-components-ios,samnm/material-components-ios,material-components/material-components-ios,willlarche/material-components-ios,samnm/material-components-ios,Eccelor/material-components-ios,sigito/material-components-ios,chriscox/material-components-ios,brianjmoore/material-components-ios,brianjmoore/material-components-ios,chriscox/material-components-ios,sigito/material-components-ios,sigito/material-components-ios,randallli/material-components-ios,Eccelor/material-components-ios,brianjmoore/material-components-ios,material-components/material-components-ios,randallli/material-components-ios,samnm/material-components-ios,randallli/material-components-ios,chriscox/material-components-ios,Eccelor/material-components-ios,willlarche/material-components-ios