remove broken conditional in discussion entry replies

fixes CNVS-14139

test plan:
 * run rails 3
 * create a discussion associated with an assignment
 * in the database, change the created_at for the discussion_topic
   to over two weeks ago
 * post multiple replies to a discussion
 * it should not fail or log an error_report

Change-Id: I1e8960b7277f373c818fdcb95a37dba9933f7188
Reviewed-on: https://gerrit.instructure.com/37485
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: James Williams  <jamesw@instructure.com>
QA-Review: August Thornton <august@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>