Disregard incoming messages after WebMIDI has been cycled on/off

Unfortunately, unregistering the event handlers does nothing to stop incoming
incoming MIDI messages from external devices from being received and handled,
nor does it seem to be possible to stop the system from registering and
working with newly connected devices. Just ignoring these messages as long as
"useWebMidi" is false seems to be the best/only solution.

src/components/WebMidi.svelte

@@ -1,7 +1,7 @@
 <script>
   import { onMount } from "svelte";
   import { clamp } from "../lib/utils";
-  import { midiInputs, midiOutputs } from "../stores";
+  import { midiInputs, midiOutputs, userSettings } from "../stores";
 
   export let startNote;
   export let stopNote;
@@ -27,7 +27,7 @@
   };
 
   const receiveMidiMsg = ({ data: [msgType, entity, value] }) => {
-    if (!entity) return;
+    if (!entity || !$userSettings.useWebMidi) return;
 
     switch (msgType) {
       case midiBytes.CONTROLLER:
@@ -87,12 +87,6 @@
         midi.onstatechange = () => updatePorts(midi);
       });
     }
-
-    return () => {
-      $midiInputs.forEach((input) =>
-        input.removeEventListener("midimessage", receiveMidiMsg),
-      );
-    };
   });
 
   export { sendMidiMsg };