remove sgsn, gbproxy and gtphub from openbsc.git

The GPRS related programs osmo-sgsn, osmo-gtphub and osmo-gbproxy
have been split off into the separate osmo-sgsn repository, which
can be found at
	git://git.osmocom.org/osmo-sgsn.git
	http://git.osmocom.org/osmo-sgsn/

This is technically unrelated but conceptually part of the larger
NITB-split activities.

I did a brief log of all changes in src/gprs and couldn't find any
commits that we might have applied here but which are missing from
osmo-sgsn.git.

Change-Id: If60e28b23f5cfb2c4eb354951363a2bb63f3e0de
124 files changed
tree: 39aeda51387ba5af9ebd44a552163fa0d0345e52
  1. contrib/
  2. debian/
  3. openbsc/
  4. .gitignore
  5. .gitreview
  6. .mailmap