load fewer contexts when course admins message a group
load fewer contexts when course admins message a group

fixes CNVS-21686

test plan
- regression test sending messages to groups in conversations

Change-Id: Ic8043fcf44ed1d190aff96084a1aa91fba4467b7
Reviewed-on: https://gerrit.instructure.com/59377
Reviewed-by: Alex Boyd <6bb5a335b0b6c251e818c0de653d342158f949f9@instructure.com>
Tested-by: Jenkins
Reviewed-by: Steven Burnett <a0b450117c5d20a22d5c4d52bb8ae13adee003d8@instructure.com>
QA-Review: Heath Hales <8ca81b68c7e2592ac614bd07f22fcc735ca55f93@instructure.com>
Product-Review: Joel Hough <4816dabf8db1bc6cac35b3a24cab2ff844b5b0c7@instructure.com>

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