faculty journal: don't title every private message "Today"

fixes CNVS-11579

test plan:
  * enable faculty journal
  * open old conversations
  * compose a private message to a student
  * check "Add as a Faculty Journal entry"
  * send the message
  * open the student's faculty journal
  * verify that the journal entry is not titled with "Today"

Change-Id: If7ee55a4c6f9839b5828157a57554d74155db3ca
Reviewed-on: https://gerrit.instructure.com/31804
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Joel Hough <joel@instructure.com>
QA-Review: Steven Shepherd <sshepherd@instructure.com>
Product-Review: Braden Anderson <banderson@instructure.com>