help: Update "Mark all messages as read" for Flutter launch.

Deletes static/images/help/mobile-globe-icon.svg as it's no
longer used.

Part of #34748.

help/marking-messages-as-read.md

@@ -105,16 +105,15 @@ channel or topic as read**.
 {tab|mobile}
 
 1. Tap a channel, topic, or the **Combined feed**
-   (<img src="/static/images/help/mobile-globe-icon.svg" alt="globe" class="help-center-icon"/>)
-   tab.
+   (<i class="zulip-icon zulip-icon-all-messages mobile-help"></i>) tab.
 
-2. Tap **Mark channel as read**, **Mark topic as read**, or **Mark all as read**
-   near the top right corner of the app.
+2. Scroll down to the bottom of the message view, and tap **Mark all messages
+   as read**.
 
 !!! tip ""
 
-    You can also press and hold a topic until the long-press menu appears, and
-    select **Mark topic as read**.
+    You can also press and hold a channel or topic until the long-press menu
+    appears, and select the option to mark as read.
 
 {end_tabs}
 

static/images/help/mobile-globe-icon.svg

@@ -1,5 +0,0 @@
-<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="none" stroke="#6492fd" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="feather feather-globe">
-    <circle cx="12" cy="12" r="10"></circle>
-    <line x1="2" y1="12" x2="22" y2="12"></line>
-    <path d="M12 2a15.3 15.3 0 0 1 4 10 15.3 15.3 0 0 1-4 10 15.3 15.3 0 0 1-4-10 15.3 15.3 0 0 1 4-10z"></path>
-</svg>