promenu: register swipe as part of setUI

... for removing later, e.g. when a submenu comes along

apps/promenu/bootb2.js

@@ -150,16 +150,21 @@ E.showMenu = function (items) {
         else if (backItem && "back" in backItem)
             back = backItem.back;
     }
+    var onSwipe;
     if (typeof back === "function") {
         var back_1 = back;
-        Bangle.on('swipe', function (lr, _ud) {
+        onSwipe = function (lr) {
             if (lr < 0)
                 back_1();
-        });
+        };
+        Bangle.on('swipe', onSwipe);
     }
     Bangle.setUI({
         mode: "updown",
         back: back,
+        remove: function () {
+            Bangle.removeListener("swipe", onSwipe);
+        },
     }, function (dir) {
         if (dir)
             l.move(dir);

apps/promenu/bootb2.ts

@@ -170,17 +170,21 @@ type ActualMenuItem = Exclude<Menu["..."], MenuOptions | undefined>;
     else if (backItem && "back" in backItem)
       back = backItem.back;
   }
+  let onSwipe: SwipeCallback | undefined;
   if (typeof back === "function") {
     const back_ = back;
-    Bangle.on('swipe', (lr, _ud) => {
+    onSwipe = (lr/*, ud*/) => {
       if (lr < 0) back_();
-    })
+    };
+    Bangle.on('swipe', onSwipe);
   }
 
-  Bangle.setUI(
-      {
+  Bangle.setUI({
           mode: "updown",
           back,
+          remove: () => {
+              Bangle.removeListener("swipe", onSwipe);
+          },
       } as SetUIArg<"updown">,
       dir => {
           if (dir) l.move(dir);