Fix the use of MobX in playground (#5294)

* Register new playground component onMount

* No need of observer

* Fix tests

js/src/playground/store.js

@@ -14,12 +14,12 @@
 // You should have received a copy of the GNU General Public License
 // along with Parity.  If not, see <http://www.gnu.org/licenses/>.
 
-import { action, observable } from 'mobx';
+import { action } from 'mobx';
 
 let instance = null;
 
 export default class PlaygroundStore {
-  @observable components = [];
+  components = [];
 
   static get () {
     if (!instance) {
@@ -35,17 +35,6 @@ export default class PlaygroundStore {
 
   @action
   add (component) {
-    const name = component.type.displayName || component.type.name;
-    const hasComponent = this.components.find((c) => {
-      const cName = c.type.displayName || c.type.name;
-
-      return name && cName && cName === name;
-    });
-
-    if (hasComponent) {
-      return;
-    }
-
     this.components.push(component);
   }
 }

js/src/playground/store.spec.js

@@ -31,11 +31,4 @@ describe('playground/store', () => {
     PlaygroundStore.register(<QrCode />);
     expect(store.components.length).greaterThan(0);
   });
-
-  it('adds new Components only once', () => {
-    PlaygroundStore.register(<QrCode />);
-    PlaygroundStore.register(<QrCode />);
-
-    expect(store.components.filter((c) => /QrCode/i.test(c.type.name)).length).equal(1);
-  });
 });