[web] [refactor] [ENG-716] destructure props in confirm-leave-thread-modal

Summary:
just moving props to a destructure on top of file

https://linear.app/comm/issue/ENG-716/introduce-leave-channel-modal

Test Plan: click leave button

Reviewers: atul

Reviewed By: atul

Subscribers: ashoat, palys-swm, Adrian, karol-bisztyga, yayabosh

Differential Revision: https://phabricator.ashoat.com/D3613