Remove no longer used struct OSPropertiesDeltas

* Also noted that we enqueue only one Properties Delta change at a time - for example, one of session_time, session_count, or purchases - so the struct OSPropertiesDeltas is not needed. It was always being created with only 1 property and the rest being nil.
* Now that these properties deltas are going to be combined together, we are not using this struct anymore anyways.

Author: nan-li

iOS_SDK/OneSignalSDK/OneSignalUser/Source/OSPropertiesModel.swift

@@ -29,22 +29,6 @@ import Foundation
 import OneSignalOSCore
 import OneSignalCore
 
-struct OSPropertiesDeltas {
-    let sessionTime: NSNumber?
-    let sessionCount: NSNumber?
-    let amountSpent: NSNumber?
-    let purchases: [[String: AnyObject]]?
-
-    func jsonRepresentation() -> [String: Any] {
-        var deltas = [String: Any]()
-        deltas["session_count"] = sessionCount
-        deltas["session_time"] = sessionTime?.intValue // server expects an int
-        deltas["amountSpent"] = amountSpent
-        deltas["purchases"] = purchases
-        return deltas
-    }
-}
-
 // Both lat and long must exist to be accepted by the server
 class OSLocationPoint: NSObject, NSCoding {
     let lat: Float