tests/lcitool: Remove g++ from the containers (except for the MinGW one)

tests/lcitool: Remove g++ from the containers (except for the MinGW one)

We don't need C++ for the normal QEMU builds anymore, so installing
g++ in each and every container seems to be a waste of time and disk
space. The only container that still needs it is the Fedora MinGW
container that builds the only remaining C++ code in ./qga/vss-win32/
and we can install it there with an extra project yml file instead.

Message-ID: <20240516084059.511463-4-thuth@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>