Always keep the compose box open after sending.

(Some cases are disabled on outside of staging still due to mix
protection concerns).

(imported from commit 26fcb95c055640ddd87c5df424990ebd865a336a)

zephyr/static/js/zephyr.js

@@ -10,7 +10,6 @@ var queued_mark_as_read = [];
 var queued_flag_timer;
 
 var respond_to_cursor = false;
-var respond_to_sent_message = false;
 
 var get_updates_params = {
     pointer: -1