staging: ion: remove from the tree

staging: ion: remove from the tree

The ION android code has long been marked to be removed, now that we
dma-buf support merged into the real part of the kernel.

It was thought that we could wait to remove the ion kernel at a later
time, but as the out-of-tree Android fork of the ion code has diverged
quite a bit, and any Android device using the ion interface uses that
forked version and not this in-tree version, the in-tree copy of the
code is abandonded and not used by anyone.

Combine this abandoned codebase with the need to make changes to it in
order to keep the kernel building properly, which then causes merge
issues when merging those changes into the out-of-tree Android code, and
you end up with two different groups of people (the in-kernel-tree
developers, and the Android kernel developers) who are both annoyed at
the current situation.  Because of this problem, just drop the in-kernel
copy of the ion code now, as it's not used, and is only causing problems
for everyone involved.

Cc: "Arve Hjønnevåg" <arve@android.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: Christian Brauner <christian@brauner.io>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Hridya Valsaraju <hridya@google.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Laura Abbott <laura@labbott.name>
Cc: Martijn Coenen <maco@android.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Todd Kjos <tkjos@android.com>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Link: https://lore.kernel.org/r/20200827123627.538189-1-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>