package/pkg-golang: default to rawname to install binaries

The default currently is to rely on the package name to decide what to
build and install if not specified by the caller. This works nice for
target packages, where a 'foo' package will by default build and
install a 'foo' executable.

However, for host packages, that will build and install a 'host-foo'
exzcutable, which is not really, even really not, what would be
expected.

We fix that by using the package raw name, i.e. the package name with
the host- prefix yanked away.

It is very improbable that there already are many host-golang packages in
the wild (in br2-external trees), but if there are, they would forcibly
define those variables to a sane value.  This change is not incompatible, as
the values provided by packages take precedence; it's just that those
packages now carry superfluous, if innocuous, variable assignments.

Signed-off-by: Yann E. MORIN <yann.morin@orange.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>