Image paste modal cleanup

Summary: Removed extraneous styles and closing tags.

Test Plan: Tested on iOS and everything looks and works the same.

Reviewers: ashoat, palys-swm

Reviewed By: ashoat

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

Differential Revision: https://phabricator.ashoat.com/D723