FROMLIST: staging: greybus: drop loopback test files

The greybus loopback test tool does not belong burried down in a
driver-specific directory.  If it is needed, it should be somewhere
else, like in the testing directory.  But as the loopback driver is
probably never going to be merged out of the staging directory, let's
just delete the test alltogether for now.  If it's needed in the future,
it can be brought back with a revert.

Also, having an Android.mk file in the kernel source tree breaks some
Android build systems when trying to build from a read-only source tree,
the report of which prompted this being a good reason to remove it as
well.

Cc: Johan Hovold <johan@kernel.org>
Cc: Alex Elder <elder@kernel.org>
Cc: Jack Schofield <schofija@oregonstate.edu>
Cc: Vaibhav Nagare <vnagare@redhat.com>
Cc: greybus-dev@lists.linaro.org
Change-Id: Ie19bcd87d0062d8453ff0d3d998224a7e478f3d0
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Bug: 275824813
Link: https://lore.kernel.org/r/2023040613-huntsman-goldsmith-4a41@gregkh


Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>