[macOS] Eliminate extraneous loadView calls (#47166)

Eliminate unnecessary calls to [NSViewController loadView]. To quote the [documentation][loadview] for this method: "Do not call this method. If you require this method to be called, access the view property."

In several of the existing tests, we do read viewController.view, and the other tests pass without this line regardless.

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

shell/platform/darwin/macos/framework/Source/AccessibilityBridgeMacTest.mm

@@ -61,7 +61,6 @@ @implementation AccessibilityBridgeTestViewController
 TEST(AccessibilityBridgeMacTest, SendsAccessibilityCreateNotificationToWindowOfFlutterView) {
   FlutterViewController* viewController = CreateTestViewController();
   FlutterEngine* engine = viewController.engine;
-  [viewController loadView];
 
   NSWindow* expectedTarget = [[NSWindow alloc] initWithContentRect:NSMakeRect(0, 0, 800, 600)
                                                          styleMask:NSBorderlessWindowMask
@@ -122,7 +121,6 @@ @implementation AccessibilityBridgeTestViewController
 TEST(AccessibilityBridgeMacTest, NonZeroRootNodeId) {
   FlutterViewController* viewController = CreateTestViewController();
   FlutterEngine* engine = viewController.engine;
-  [viewController loadView];
 
   NSWindow* expectedTarget = [[NSWindow alloc] initWithContentRect:NSMakeRect(0, 0, 800, 600)
                                                          styleMask:NSBorderlessWindowMask
@@ -192,7 +190,7 @@ @implementation AccessibilityBridgeTestViewController
 TEST(AccessibilityBridgeMacTest, DoesNotSendAccessibilityCreateNotificationWhenHeadless) {
   FlutterViewController* viewController = CreateTestViewController();
   FlutterEngine* engine = viewController.engine;
-  [viewController loadView];
+
   // Setting up bridge so that the AccessibilityBridgeMacDelegateSpy
   // can query semantics information from.
   engine.semanticsEnabled = YES;
@@ -238,7 +236,6 @@ @implementation AccessibilityBridgeTestViewController
 TEST(AccessibilityBridgeMacTest, DoesNotSendAccessibilityCreateNotificationWhenNoWindow) {
   FlutterViewController* viewController = CreateTestViewController();
   FlutterEngine* engine = viewController.engine;
-  [viewController loadView];
 
   // Setting up bridge so that the AccessibilityBridgeMacDelegateSpy
   // can query semantics information from.