staging: gasket: remove TODO item about SPDX usage

Now that the files are all properly tagged with SPDX lines, and the
boilerplate license text is gone, remove the TODO item.

Cc: Rob Springer <rspringer@google.com>
Cc: John Joseph <jnjoseph@google.com>
Cc: Ben Chan <benchan@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/gasket/TODO

 This is a list of things that need to be done to get this driver out of the
 staging directory.
-- Use SPDX tags to show the license of the file, and no more "boiler-plate"
-  license text is needed.
 - Remove static function declarations.
 - Document sysfs files with Documentation/ABI/ entries.
 - Use misc interface instead of major number for driver version description.