mgw: Remove hack in f_two_crcx_mdcx_and_rtp_osmux() no longer needed

Since osmo-mgw.git 2177919edb3bc0dd308be388272486ffd97f4761, osmo-mgw can handle
properly conns containing a different remote and local CID.
Hence this hack can be dropped.

Related: SYS#5987
Change-Id: I531631d716581f68c11d3c0b07fc6755a822a0d3
1 file changed