[lib] Avoid using Object.fromEntries

Summary: This is the only place where it's used so we can simply remove it instead of adding a polyfill

Test Plan: Open pending thread, send a message and check if it was created correctly

Reviewers: ashoat

Reviewed By: ashoat

Subscribers: KatPo, zrebcu411, Adrian, atul, subnub, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D716