staging: remove hp100 driver

It's old, obsolete, and no one wants to take care of it anymore.

It's been in staging for 5 months with no one paying attention to it, so
let's just delete it for now.

If someone has this hardware, and wants the driver back, the deletion
can be easily reverted.

Cc: Joe Perches <joe@perches.com>
Cc: Jaroslav Kysela <perex@perex.cz>
Link: https://lore.kernel.org/r/20200326080233.978323-1-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>