Removed unnecessary @synthesize and use property accessor

Trivial cleanup. No functional change.

Change-Id: I28a0579ce2edebbac5197c7730b7f48099d22239
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1614780
Auto-Submit: Peter Lee <pkl@chromium.org>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#660313}

ios/chrome/browser/ui/content_suggestions/content_suggestions_coordinator.mm

@@ -69,17 +69,6 @@
 @implementation ContentSuggestionsCoordinator
 
 @synthesize browserState = _browserState;
-@synthesize suggestionsViewController = _suggestionsViewController;
-@synthesize visible = _visible;
-@synthesize contentSuggestionsMediator = _contentSuggestionsMediator;
-@synthesize headerCollectionInteractionHandler =
-    _headerCollectionInteractionHandler;
-@synthesize headerController = _headerController;
-@synthesize webStateList = _webStateList;
-@synthesize toolbarDelegate = _toolbarDelegate;
-@synthesize dispatcher = _dispatcher;
-@synthesize metricsRecorder = _metricsRecorder;
-@synthesize NTPMediator = _NTPMediator;
 
 - (void)start {
   if (self.visible || !self.browserState) {
@@ -116,7 +105,7 @@
   }
 
   UrlLoadingService* urlLoadingService =
-      UrlLoadingServiceFactory::GetForBrowserState(_browserState);
+      UrlLoadingServiceFactory::GetForBrowserState(self.browserState);
 
   self.NTPMediator = [[NTPHomeMediator alloc]
       initWithWebStateList:self.webStateList