overview: fix graph "OsmoMGW used with OsmoMSC"

The graph "OsmoMGW used with OsmoMSC" shows a BSC entity that accepts
AoIP and RTP, however osmo-bsc has no RTP proxy functionality. It makes
probably more sense to remove the BTS from the graph and call "BSC" "2G
BSS"

Change-Id: I6c7d26b6e45d0f953b82bca3ae7b2f26600982b2
1 file changed