Fix tests

Author: sbarrio

packages/core/android/src/test/kotlin/com/datadog/reactnative/DdRumTest.kt

@@ -536,7 +536,7 @@ internal class DdRumTest {
         // When
         testedDdRum.reportAppFullyDisplayed(mockPromise)
 
-        // Then 
+        // Then
         verify(mockRumMonitor).reportAppFullyDisplayed()
     }
 

packages/core/ios/Tests/MockRUMMonitor.swift

@@ -10,10 +10,6 @@
 @testable import DatadogSDKReactNative
 
 internal class MockRUMMonitor: RUMMonitorProtocol {
-    func reportAppFullyDisplayed() {
-        // not implemented
-    }
-    
     func currentSessionID(completion: @escaping (String?) -> Void) {
         // not implemented
     }