popovers: Change "Delete all messages in topic" to "Delete topic".

This cleans up the copy a bit to be more readable.

Documentation changes cleaned up by tabbott.

Fixes #16856.

docs/overview/changelog.md

@@ -790,7 +790,7 @@ and is enabled by default in that case. To disable it, set
   New authentication backends supported by python-social-auth can now be
   added with just a few dozen lines of code.
 - Added API documentation for user groups and custom emoji.
-- Administrators can now easily delete all messages in a topic.
+- Administrators can now easily delete a topic.
 - Added display of a user's role (administrator, guest, etc.) in
   various relevant places.
 - Added support for sending "topic" rather than the legacy "subject"

static/templates/delete_topic_modal.hbs

@@ -7,13 +7,13 @@
         </h3>
     </div>
     <div class="modal-body">
-        <p>{{#tr this}}Are you sure you want to permanently delete all messages in <b>__topic_name__</b>?{{/tr}}</p>
+        <p>{{#tr this}}Are you sure you want to permanently delete <b>__topic_name__</b>?{{/tr}}</p>
         <p>{{t "Deleting a topic will immediately remove it and its messages for everyone. Other users may find this confusing, especially if they had received an email or push notification related to the deleted messages." }}</p>
     </div>
     <div class="modal-footer">
         <button class="button" data-dismiss="modal">{{t "Cancel" }}</button>
         <button class="button btn-danger rounded" id="do_delete_topic_button">
-            {{t "Delete messages" }}
+            {{t "Delete topic" }}
         </button>
     </div>
 </div>

static/templates/topic_sidebar_actions.hbs

@@ -58,7 +58,7 @@
     <li>
         <a tabindex="0" class="sidebar-popover-delete-topic-messages" data-stream-id="{{ stream_id }}" data-topic-name="{{ topic_name }}">
             <i class="fa fa-trash" aria-hidden="true"></i>
-            {{t "Delete all messages in topic"}}
+            {{t "Delete topic"}}
         </a>
     </li>
     {{/if}}

templates/zerver/help/delete-a-topic.md

@@ -26,14 +26,15 @@ whereas [deleting a stream](/help/delete-a-stream) does not.
 
 1. Click the ellipsis (<i class="zulip-icon ellipsis-v-solid"></i>).
 
-1. Click **Delete all messages in `<topic>`**.
+1. Click **Delete topic**.
 
-1. Click **Delete messages**.
+1. Click **Delete topic** in the confirmation dialog.
 
 {end_tabs}
 
-Note that deleting the last message with a particular topic also deletes
-that topic.
+Note that deleting all of the individual messages within a particular
+topic also deletes that topic. Structurally, topics are simply an
+attribute of messages in Zulip.
 
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