tools: ynl: remove generated user space code from git

The ynl-generated user space C code is already above 25kLoC
and is growing.

The initial reason to commit these files was to make reviewing changes
to the generator easier. Unfortunately, it has the opposite effect on
reviewing changes to specs, and we get far more changes to specs
than to the generator.

Uncommit those fails, as they are generated on the fly as needed.
netdev patchwork now runs a script on each series to create a diff
of generated code on the fly, for the rare cases when looking at
it is helpful:
https://github.com/kuba-moo/nipa/blob/master/tests/series/ynl/ynl.sh



Suggested-by: Paolo Abeni <pabeni@redhat.com>
Acked-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>