refactor: remote admin channel validation

app/src/main/java/com/geeksville/mesh/model/UIState.kt

@@ -423,9 +423,8 @@ class UIViewModel @Inject constructor(
         }
     }
 
-    val adminChannelIndex: Int /** matches [MeshService.adminChannelIndex] **/
-        get() = channelSet.settingsList.indexOfFirst { it.name.equals("admin", ignoreCase = true) }
-            .coerceAtLeast(0)
+    val hasAdminChannel: Boolean
+        get() = channelSet.settingsList.any { it.name.equals("admin", ignoreCase = true) }
 
     /**
      * Write the persisted packet data out to a CSV file in the specified location.

app/src/main/java/com/geeksville/mesh/ui/UsersFragment.kt

@@ -101,7 +101,7 @@ class UsersFragment : ScreenFragment("Users"), Logging {
             if (!model.isConnected()) return
             val node = nodes[position]
             val user = node.user ?: return
-            val showAdmin = position == 0 || model.adminChannelIndex > 0
+            val showAdmin = position == 0 || model.hasAdminChannel
             val isIgnored = ignoreIncomingList.contains(node.num)
             val popup = PopupMenu(requireContext(), view)
             popup.inflate(R.menu.menu_nodes)