Replace usage of removed `store.isSidebar` selector

src/sidebar/services/streamer.js

@@ -52,7 +52,7 @@ export default function Streamer(
         break;
     }
 
-    if (!store.isSidebar()) {
+    if (store.route() !== 'sidebar') {
       applyPendingUpdates();
     }
   }

src/sidebar/services/test/streamer-test.js

@@ -123,11 +123,11 @@ describe('Streamer', function() {
           userid: 'jim@hypothes.is',
         },
       }),
-      isSidebar: sinon.stub().returns(true),
       pendingUpdates: sinon.stub().returns({}),
       pendingDeletions: sinon.stub().returns({}),
       receiveRealTimeUpdates: sinon.stub(),
       removeAnnotations: sinon.stub(),
+      route: sinon.stub().returns('sidebar'),
     };
 
     fakeGroups = {
@@ -275,7 +275,7 @@ describe('Streamer', function() {
 
     context('when the app is the stream', function() {
       beforeEach(function() {
-        fakeStore.isSidebar.returns(false);
+        fakeStore.route.returns('stream');
       });
 
       it('applies updates immediately', function() {