[web] Remove duplicate CSS properties within same selector

Summary:
Kept running across duplicate properties in CSS selectors and "sneaking in" their removal into other diffs. Just went ahead and cut all of them.

The last instance of the property within the selector is what "wins," so I just cut the instances that came before.

Test Plan: Shouldn't make a difference, basically no-op.

Reviewers: benschac, palys-swm, ashoat

Reviewed By: benschac, ashoat

Subscribers: Adrian, karol-bisztyga, yayabosh

Differential Revision: https://phabricator.ashoat.com/D3588