[native] switch getViewerAlreadySelectedMessageReactions to useGetViewerAlreadySelectedMessageReactions

Summary: small follow up diff to address comment in D8288

Test Plan: confirmed that the already selected emojis still behaved as expected in the emoji keyboard

Reviewers: atul, kamil

Reviewed By: kamil

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8410