Remove deprecated method from Unity interface

Summary:
This wrapper was missed during the cleanup when moving to v12 (it was marked as deprecated in v11 so was deleted in v12).

I'm not sure how the previous build for unity sdk diffs were compiling (maybe it's a specific xcode thing?) but removing this is better

Reviewed By: WardMeta

Differential Revision: D35568679

fbshipit-source-id: 79bcc0f644c741c707be5d9c37d690ea57b2c4f2

Facebook.Unity.IOS/IOSWrapper.cs

@@ -543,12 +543,6 @@ private static extern void IOSFBSetDataProcessingOptions(
             int country,
             int state);
 
-        [DllImport("__Internal")]
-        private static extern void IOSFBUpdateUserProperties(
-            int numParams,
-            string[] paramKeys,
-            string[] paramVals);
-
         [DllImport("__Internal")]
         private static extern string IOSFBCurrentAuthenticationToken();