iOS: Fix flaky tests (remove timeouts) (#55961)

When run repeatedly, some of the iOS unit tests can relatively easily
blow their test timeouts. Since we're testing behaviour and not
performance in these tests there's no need to enforce a particular
timeout.

The bots will fail if the tests timeout, regardless.

Author: cbracken

shell/platform/darwin/ios/framework/Source/FlutterEngineTest.mm

@@ -249,7 +249,7 @@ - (void)testWaitForFirstFrameTimeout {
                        [timeoutFirstFrame fulfill];
                      }
                    }];
-  [self waitForExpectationsWithTimeout:5 handler:nil];
+  [self waitForExpectations:@[ timeoutFirstFrame ]];
 }
 
 - (void)testSpawn {
@@ -275,7 +275,7 @@ - (void)testDeallocNotification {
                                  [deallocNotification fulfill];
                                }];
   }
-  [self waitForExpectationsWithTimeout:1 handler:nil];
+  [self waitForExpectations:@[ deallocNotification ]];
   [center removeObserver:observer];
 }
 
@@ -299,7 +299,7 @@ - (void)testSetHandlerAfterRun {
                                  [gotMessage fulfill];
                                }];
   });
-  [self waitForExpectationsWithTimeout:1 handler:nil];
+  [self waitForExpectations:@[ gotMessage ]];
 }
 
 - (void)testThreadPrioritySetCorrectly {
@@ -325,7 +325,7 @@ - (void)testThreadPrioritySetCorrectly {
 
   FlutterEngine* engine = [[FlutterEngine alloc] init];
   [engine run];
-  [self waitForExpectationsWithTimeout:1 handler:nil];
+  [self waitForExpectations:@[ prioritiesSet ]];
 
   method_setImplementation(method, originalSetThreadPriority);
 }