queue_processor: Remove unreachable code.
queue_processor: Remove unreachable code.

This change was added in
https://github.com/zulip/zulip/commit/c93f1d4eda71ddcca5ba05d0bf9fbfc8895829e2#diff-d88010b113b79080cab5885fdfbbb56ae2d380cb601d8f520621b3361ad8cebc.
`message.content` cannot be `None` by the model definition.

Signed-off-by: Zixuan James Li <74923aee05c23ca90566381b5d6b0cd9451b6054@gmail.com>

rht/zulip,rht/zulip,zulip/zulip,andersk/zulip,andersk/zulip,rht/zulip,zulip/zulip,andersk/zulip,rht/zulip,rht/zulip,rht/zulip,andersk/zulip,zulip/zulip,zulip/zulip,zulip/zulip,andersk/zulip,rht/zulip,zulip/zulip,andersk/zulip,andersk/zulip,zulip/zulip