Move (test) RtpFileReader to a lightweight target.

Moves RtpFileReader to rtp_packet_parser and renames it to
rtp_test_utils which is allowed to rely on rtp_rtcp.

R=andrew@webrtc.org
BUG=

Review URL: https://webrtc-codereview.appspot.com/24979004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7536 4adac7df-926f-26a2-2b94-8c16560cd09d