refactor(picker): remove usless code

src/components/picker/picker.vue

@@ -241,10 +241,9 @@
             swipeTime: this.swipeTime,
             observeDOM: false
           })
-          wheel._cube_scrollEnd = () => {
+          wheel.on('scrollEnd', () => {
             this.$emit(EVENT_CHANGE, i, wheel.getSelectedIndex())
-          }
-          wheel.on('scrollEnd', wheel._cube_scrollEnd)
+          })
         } else {
           this.wheels[i].refresh()
         }
@@ -255,9 +254,7 @@
         if (this.wheels.length > dataLength) {
           const extraWheels = this.wheels.splice(dataLength)
           extraWheels.forEach((wheel) => {
-            wheel.off('scrollEnd', wheel._cube_scrollEnd)
             wheel.destroy()
-            wheel._cube_scrollEnd = null
           })
         }
       },
@@ -269,9 +266,7 @@
     },
     beforeDestroy() {
       this.wheels && this.wheels.forEach((wheel) => {
-        wheel.off('scrollEnd', wheel._cube_scrollEnd)
         wheel.destroy()
-        wheel._cube_scrollEnd = null
       })
       this.wheels = null
     },