MAP: Fix IOT specific msgListing issue with BenzCarkit.

Benz NTG4.5 carkit in MCE role fail to list messages
when Messages-Listing XML object include standalone,
encoding and xml version flags in the beginning of
final XML output.
Add a IOT specific check to remove these flags before
responding with  final messagesList from MSE.

Change-Id: I4d0d6e4a86538a04a576c7d138a85ed5233b4cf3
CRs-Fixed: 903463