Clean up #pragma warning disable by marking as Obsolete

Author: keveleigh

Assets/MRTK/Core/Utilities/WindowsApiChecker.cs

@@ -21,11 +21,11 @@ namespace Microsoft.MixedReality.Toolkit.Windows.Utilities
     /// </remarks>
     public static class WindowsApiChecker
     {
+        [Obsolete("The CheckApiContracts method is obsolete (and should not need to be called manually regardless) and will be removed from a future version of MRTK. Please use IsMethodAvailable(), IsPropertyAvailable() or IsTypeAvailable().")]
         [RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.BeforeSceneLoad)]
         public static void CheckApiContracts()
         {
             // Disable the obsolete warning to enable setting the properties for legacy code.
-#pragma warning disable 0618
 #if WINDOWS_UWP
             UniversalApiContractV8_IsAvailable = ApiInformation.IsApiContractPresent("Windows.Foundation.UniversalApiContract", 8);
             UniversalApiContractV7_IsAvailable = ApiInformation.IsApiContractPresent("Windows.Foundation.UniversalApiContract", 7);
@@ -41,7 +41,6 @@ public static void CheckApiContracts()
             UniversalApiContractV4_IsAvailable = false;
             UniversalApiContractV3_IsAvailable = false;
 #endif // WINDOWS_UWP
-#pragma warning restore 0618
         }
 
         /// <summary>