help: Update "Mute or unmute a topic" for Flutter launch.

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

Part of #34748.

help/mute-a-topic.md

@@ -39,19 +39,16 @@
 
 {tab|mobile}
 
-1. Tap the **Channels**
-   (<img src="/static/images/help/mobile-hash-icon.svg" alt="hash" class="help-center-icon"/>)
+1. Tap the **Channels** (<i class="zulip-icon zulip-icon-hash mobile-help"></i>)
    tab at the bottom of the app.
 
 1. Select a channel containing topics you want to configure.
 
-1. Tap the **Topics list**
-   (<img src="/static/images/help/mobile-list-icon.svg" alt="list" class="help-center-icon"/>)
-   icon in the upper right corner of the app.
+1. Tap **topics** in the upper right corner of the app.
 
 {!topic-long-press-menu.md!}
 
-1. Tap **Mute topic** or **Unmute topic**.
+1. Tap **Mute topic**, **Unmute topic**, or **Follow topic**.
 
 !!! tip ""
 

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

@@ -1 +0,0 @@
-<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#000000" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="feather feather-list"><line x1="8" y1="6" x2="21" y2="6"></line><line x1="8" y1="12" x2="21" y2="12"></line><line x1="8" y1="18" x2="21" y2="18"></line><line x1="3" y1="6" x2="3.01" y2="6"></line><line x1="3" y1="12" x2="3.01" y2="12"></line><line x1="3" y1="18" x2="3.01" y2="18"></line></svg>