docs: msgbox icons are always shown since we're using appimage based …

…on ubuntu

docs/index.html

@@ -6815,7 +6815,6 @@ <h2 class="calibre9"><span class="calibre23">The "Last Found" Window </span></h2
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  <p class="calibre8">For example, to specify a SYSTEMMODAL box with the YES/NO buttons the <em class="calibre21">Options</em> value would be 4096+4 (4100).</p>
- <p class="calibre8 x11">The icon options change the actual icon only on Ubuntu-based systems. On other distros, there is never any image on MsgBox.</p>
  <p class="calibre8">To determine which button the user pressed in the most recent MsgBox, use the <a href="#IfMsgBox.htm" class="pcalibre3 pcalibre1 pcalibre calibre5 pcalibre2">IfMsgBox</a> command.</p>
  <p class="calibre8">The text on the buttons can be changed by following <a href="#MsgBoxButtonNames.htm" class="pcalibre3 pcalibre1 pcalibre calibre5 pcalibre2">this example</a>.</p>
  <p class="calibre8"> <span class="rm">The windows shown by this command are a built-in feature of Windows.</span> As such, the X button (close) in the title bar is enabled only when certain buttons are present in the dialog: If there is only an OK button, clicking the X button is the same as pressing OK. Otherwise, the X button is disabled unless there is a Cancel button, in which case clicking the X is the same as pressing Cancel. <span class="x11">Pressing Escape on a window without a X still closes the window as if a fictional Cancel button were pressed.</span></p>