[lib] Stop shimming Blob-hosted multimedia messages

Summary: Points 3a and 3b from ENG-6459.

Test Plan: Replaced next code version constant with a past version and verified that robotext no longer appears and blob-hosted media messages are displayed.

Reviewers: ashoat

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D13888