MAP: Remove extra new line while encoding messagesListing.

Remove new line included for start document FastXmlSerializer
while encoding messagesListing response. Otherwise, the newline
character was shown as special "&#10" value at MCE end due to
which later was not able to parse the response.
This modification is required as per the new feature to
encode special characters introduced from FastXmlSerializer.

CRs-Fixed: 1026392

Change-Id: Ica558b540ec05a39651ca9636ed7212748e40fe6