Remove invalid CSS border-shadow property for input.jx-tokenizer-input

Summary:
The W3C CSS validator throws Property border-shadow doesn't exist : none as that property does not exist.
See 404 on https://developer.mozilla.org/en-US/docs/Web/CSS/border-shadow

Test Plan: Paste phui-oi-list-view.css into https://jigsaw.w3.org/css-validator/; find no CSS docs for that property.

Reviewers: O1 Blessed Committers, valerio.bozzolan

Reviewed By: O1 Blessed Committers, valerio.bozzolan

Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Differential Revision: https://we.phorge.it/D25924