nativesdk-packagegroup-sdk-host.bb: remove nativesdk-dnf

nativesdk-packagegroup-sdk-host.bb: remove nativesdk-dnf

Currently the dnf command inside SDK does not work. We will
get error message like below:

  ImportError: No module named 'dnf'

So remove it from nativesdk-packagegroup-sdk-host, otherwise,
users will get unpleasant experience if they are working inside
SDK environment on some distros like Fedora.

(From OE-Core rev: a7005a4fc5f29db796b1d258b7c259b9433848ce)

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>