Revert "Add NATT keepalive resources and methods into IpSecService"

This reverts commit 4aac3e9e48.

Reason for revert: Adds dependency between IpSecService and
                   ConnectivityService may lead to future deadlock
		   problems. Uses a simpler approach instead,
		   hence the solution is not needed.
		   See aosp/954040.

Change-Id: Ibff278a6eee666cd85dba81c2bed94d568679b02

core/java/android/net/IIpSecService.aidl

@@ -72,8 +72,4 @@ interface IIpSecService
             int tunnelResourceId, int direction, int transformResourceId, in String callingPackage);
 
     void removeTransportModeTransforms(in ParcelFileDescriptor socket);
-
-    int lockEncapSocketForNattKeepalive(int encapSocketResourceId, int requesterUid);
-
-    void releaseNattKeepalive(int nattKeepaliveResourceId, int ownerUid);
 }