This also moves the methods load_mmd and load_mmd_file to
module_build_service.utils.general.
This also removes some MSE unit tests with a mix of positive and
negative streams since this is not supported in libmodulemd v2. The
user will be presented with a syntax error if they try to submit
such a modulemd file.
GenericResolver.extract_modulemd is not removed, but deprecated. Call of it
will result in a deprecation message printed. Any new code should call
load_mmd.
Signed-off-by: Chenxiong Qi <cqi@redhat.com>
