crate.settings: Remove owner by native array method splice

This fixes the following deprecations:
- The removeObject method on ember-data's PromiseManyArray is deprecated.
- The `removeObject` method on the class ManyArray is deprecated.

app/controllers/crate/settings.js

@@ -36,10 +36,12 @@ export default class CrateSettingsController extends Controller {
 
       if (owner.kind === 'team') {
         this.notifications.success(`Team ${owner.get('display_name')} removed as crate owner`);
-        this.crate.owner_team.removeObject(owner);
+        let owner_team = await this.crate.owner_team;
+        removeOwner(owner_team, owner);
       } else {
         this.notifications.success(`User ${owner.get('login')} removed as crate owner`);
-        this.crate.owner_user.removeObject(owner);
+        let owner_user = await this.crate.owner_user;
+        removeOwner(owner_user, owner);
       }
     } catch (error) {
       let subject = owner.kind === 'team' ? `team ${owner.get('display_name')}` : `user ${owner.get('login')}`;
@@ -54,3 +56,10 @@ export default class CrateSettingsController extends Controller {
     }
   });
 }
+
+function removeOwner(owners, target) {
+  let idx = owners.indexOf(target);
+  if (idx !== -1) {
+    owners.splice(idx, 1);
+  }
+}