[web] Simplify className in MessageReplyButton

Summary: In one of earlier diffs, css.tooltipRightPadding and css.tooltipLeftPadding were removed, but not from this file. Padding is added in other css, so it's safe to simplify this

Test Plan: Flow, check if visualy nothing changed

Reviewers: palys-swm, ashoat

Reviewed By: palys-swm, ashoat

Subscribers: ashoat, palys-swm, Adrian, atul

Differential Revision: https://phabricator.ashoat.com/D997