smb: smbdirect: remove unused SMBDIRECT_USE_INLINE_C_FILES logic

smb: smbdirect: remove unused SMBDIRECT_USE_INLINE_C_FILES logic

We always build as standalone module (or as part of the core kernel).

This also removes unused elements from struct smbdirect_socket
and unused exports.

Cc: Steve French <smfrench@gmail.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Long Li <longli@microsoft.com>
Cc: Namjae Jeon <linkinjeon@kernel.org>
Cc: linux-cifs@vger.kernel.org
Cc: samba-technical@lists.samba.org
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>