cifs: Remove unused inline function is_sysvol_or_netlogon()

is_sysvol_or_netlogon() is never used, so can remove it.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Signed-off-by: Steve French <stfrench@microsoft.com>