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
As PROVIDES can be used to replace real packages now, we don't need the
virtual packages as workaround anymore. This also means that the providing
packages don't need to be added to site.mk explicitly anymore when the
default provider is used.
