Re-delete zombie 'drivers/usb/serial/airprime.c' file

Stephen Rothwell points out that this file got deleted (on purpose) by
commit 640c1bc ("USB: delete airprime
driver"), but then almost immediately incorrectly resurrected by commit
95da310 ("usb_serial: API all change").

Delete it again.  If it comes back, we'll need to drive a stake through
its heart.

Reported-by: Stephen Rothwell <[email protected]>
Acked-by: Greg KH <[email protected]>
Cc: Alan Cox <[email protected]>
Cc: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: torvalds