submessage: Match style a bit more in `messages` reducer.
submessage: Match style a bit more in `messages` reducer.

Inlining these expressions gives this reducer branch the exact same
structure as most of the others of the `messages` reducer.  It also
gives the code the same structure as the data it's constructing.

vishwesh3/zulip-mobile,vishwesh3/zulip-mobile,vishwesh3/zulip-mobile,vishwesh3/zulip-mobile