staging: rtlwifi: delete the staging driver

A "real" driver for this hardware is now in the wireless-drivers-next
tree, to be merged in the next major kernel release, so this staging
driver can now be deleted as it is not needed anymore.

Note, 2 .h files remain for this driver, as they are referenced in a
separate staging driver.  That mess will be cleaned up in a follow-on
patch.

Cc: Ping-Ke Shih <pkshih@realtek.com>
Cc: Tzu-En Huang <tehuang@realtek.com>
Cc: Yan-Hsuan Chuang <yhchuang@realtek.com>
Cc: Stanislaw Gruszka <sgruszka@redhat.com>
Cc: Brian Norris <briannorris@chromium.org>
Cc: Kalle Valo <kvalo@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>