[web] [remove] text highlighting from active thread

Summary:
remove highlight on active (selected) thread screenshot (adding ashoat since atul is out today)

Test Plan: should work like before, without highlighting of text.

Reviewers: atul, ashoat

Reviewed By: ashoat

Subscribers: palys-swm, Adrian, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D3182