[web] Remove Modals usused style
Summary: The style has not been used anywhere in the project
Test Plan: Nothing changes in project
Reviewers: palys-swm, atul, benschac
Reviewed By: atul
Subscribers: ashoat, palys-swm, Adrian, atul, karol-bisztyga, benschac, yayabosh
Differential Revision: https://phabricator.ashoat.com/D3668