Staging: rtl8192u: remove api.c file

It wasn't being used, and had a hacked-up export symbol table which
wasn't very nice either.

Reported-by: James Morris <jmorris@namei.org>
Cc: Herbert Xu <herbert@gondor.hengli.com.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>