Remove broken vue-router navigation guard

Passing a callback to `next()` is only supported in `beforeRouterEnter()`, not `beforeRouterUpdate()`, so that was not doing anything this whole time.
See https://v3.router.vuejs.org/guide/advanced/navigation-guards.html#in-component-guards

Author: MetRonnie

src/mixins/subscriptionView.js

@@ -36,10 +36,5 @@ export default {
     next(vm => {
       vm.$workflowService.startSubscriptions()
     })
-  },
-  beforeRouteUpdate (to, from, next) {
-    next(vm => {
-      vm.$workflowService.startSubscriptions()
-    })
   }
 }

tests/unit/mixins/subscriptionView.spec.js

@@ -41,14 +41,4 @@ describe('Subscription View mixin', () => {
     })
     expect(workflowService.startSubscriptions.calledOnce).to.equal(true)
   })
-  it('should provide a navigation guard for when the view is updated', () => {
-    const component = Object.assign(subscriptionViewMixin)
-    const vm = {
-      $workflowService: workflowService
-    }
-    component.beforeRouteUpdate(null, null, (callback) => {
-      callback(vm)
-    })
-    expect(workflowService.startSubscriptions.calledOnce).to.equal(true)
-  })
 })