Massive removal of unused code/structs/headers

osmo-msc still had large amounts of dead code that came along from
openbsc.git.  This commit removes a lot of it, mostly stuff relevant
only to the BSC side of things (or even GPRS).

Change-Id: I247def85da2dc3ec461389fb74414a0d964e7e3c
Related: OS#2528
52 files changed