[iOS] Fix SDK deployment target to be able to compile with iOS 9.3

Fixes: https://github.com/jitsi/jitsi-meet/issues/3086

ios/sdk/src/callkit/JMCallKitEmitter.swift

 import CallKit
 import Foundation
 
+@available(iOS 10.0, *)
 internal final class JMCallKitEmitter: NSObject, CXProviderDelegate {
 
     private var listeners = Set<JMCallKitEventListenerWrapper>()
     }
 }
 
+@available(iOS 10.0, *)
 fileprivate struct JMCallKitEventListenerWrapper: Hashable {
 
     public var hashValue: Int

ios/sdk/src/callkit/JMCallKitListener.swift

 import CallKit
 import Foundation
 
+@available(iOS 10.0, *)
 @objc public protocol JMCallKitListener: NSObjectProtocol {
 
     @available(iOS 10.0, *)