The vpn-core package does not utilize simple-tc anymore.
This is now up to the VPN implementations.

Signed-off-by: David Bauer <mail@david-bauer.net>

This removes PKG_VERSION and PKG_RELEASE from most Makefiles, as the
value was never useful for Gluon packages; instead, PKG_VERSION is set
to 1 in gluon.mk.

It also removes two other weird definitions:

- gluon-iptables-clamp-mss-to-pmtu replicating the old PKG_VERSION logic
  from gluon-core, but without the fixed PKG_BUILD_DIR to prevent
  unnessary rebuilds
- gluon-hoodselector set GLUON_VERSION=3

With the removal of ramips-rt305x, the last user of
GLUON_SPECIALIZE_KERNEL is gone.