Minor cleanup in chan_sip get_msg_text() function.

Minor cleanup in chan_sip get_msg_text() function.

In r116240, get_msg_text() got an extra parameter to fix the unwanted
addition of trailing newlines to SIP MESSAGE bodies. This caused all
linefeeds to be trimmed, which isn't right either. This is a stop-gap;
the right fix is to return the original SIP request body.

Review: https://reviewboard.asterisk.org/r/1586
Reviewed by: Matt Jordan

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@346147 65c4cc65-6c06-0410-ace0-fbb531ad65f3