util: scsi: define cleanup function using VIR_DEFINE_AUTOPTR_FUNC
    
    Using the new VIR_DEFINE_AUTOPTR_FUNC macro defined in
    src/util/viralloc.h, define a new wrapper around an existing
    cleanup function which will be called when a variable declared
    with VIR_AUTOPTR macro goes out of scope. Also, drop the redundant
    viralloc.h include, since that has moved from the source module into
    the header.
    
    When variables of type virSCSIDevicePtr and virUsedByInfoPtr
    are declared using VIR_AUTOPTR, the functions virSCSIDeviceFree
    and virSCSIDeviceUsedByInfoFree, respectively, will be run
    automatically on them when they go out of scope.
    
    This commit also adds an intermediate typedef for virUsedByInfo
    type for use with the cleanup macros.
    
    Signed-off-by: Sukrit Bhatnagar <skrtbhtngr@gmail.com>
    Reviewed-by: Erik Skultety <eskultet@redhat.com>