[web] Skip loop property when dispatching updateMultimediaMessage

Summary:
Resolves 1 from ENG-9345.
We shouldn't add loop property when updating photo multimedia message. Otherwise, the DM Ops validator would reject such message.

Test Plan: Quickly-sent a DM and made sure the payload doesn't contain the loop property the DM op is processed successfully on recipient side.

Reviewers: kamil, tomek

Reviewed By: kamil

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D13419