compose: Remove now unused nonexistent_stream_reply_error.

This was a holdover from the legacy "reply" button behavior; with the
new wide button model, it just becomes a normal "compose" button.

frontend_tests/node_tests/compose.js

@@ -1764,22 +1764,6 @@ test_ui("create_message_object", (override) => {
     people.email_list_to_user_ids_string = email_list_to_user_ids_string;
 });
 
-test_ui("nonexistent_stream_reply_error", () => {
-    reset_jquery();
-
-    const actions = [];
-    $("#nonexistent_stream_reply_error").show = () => {
-        actions.push("show");
-    };
-    $("#nonexistent_stream_reply_error").hide = () => {
-        actions.push("hide");
-    };
-
-    compose.nonexistent_stream_reply_error();
-    assert.equal($("#compose-reply-error-msg").html(), "There are no messages to reply to yet.");
-    assert.deepEqual(actions, ["show", "hide"]);
-});
-
 test_ui("narrow_button_titles", () => {
     util.is_mobile = () => false;
 

static/js/click_handlers.js

@@ -641,9 +641,6 @@ export function initialize() {
     $("body").on("click", "#compose-send-status .compose-send-status-close", () => {
         $("#compose-send-status").stop(true).fadeOut(500);
     });
-    $("body").on("click", "#nonexistent_stream_reply_error .compose-send-status-close", () => {
-        $("#nonexistent_stream_reply_error").stop(true).fadeOut(500);
-    });
 
     $("body").on("click", ".empty_feed_compose_stream", (e) => {
         compose_actions.start("stream", {trigger: "empty feed message"});

static/js/compose.js

@@ -305,14 +305,6 @@ export function compose_error(error_html, bad_input) {
     }
 }
 
-export function nonexistent_stream_reply_error() {
-    $("#nonexistent_stream_reply_error").show();
-    $("#compose-reply-error-msg").html("There are no messages to reply to yet.");
-    setTimeout(() => {
-        $("#nonexistent_stream_reply_error").hide();
-    }, 5000);
-}
-
 function compose_not_subscribed_error(error_html, bad_input) {
     $("#compose-send-status")
         .removeClass(common.status_classes)

static/styles/compose.css

@@ -254,13 +254,6 @@ div[id^="message-edit-send-status"],
     margin-bottom: 10px;
 }
 
-#nonexistent_stream_reply_error {
-    padding: 8px 14px 8px 14px;
-    margin-bottom: 8px;
-    line-height: 20px;
-    display: none;
-}
-
 /* Like .alert .close */
 .send-status-close,
 .compose-send-status-close {

static/templates/compose.hbs

@@ -1,9 +1,5 @@
 <div id="compose-container">
     <div id="compose_controls" class="compose-content new-style">
-        <div id="nonexistent_stream_reply_error" class="alert-error">
-            <span class="compose-send-status-close">&times;</span>
-            <span id="compose-reply-error-msg"></span>
-        </div>
         <div id="compose_buttons">
             <span class="new_message_button reply_button_container">
                 <button type="button" class="button small rounded compose_reply_button"