staging: vt6655: remove unused functions

The IEEE11hbMgrRxAction is not exported and never used. Deleting it
allows to delete other functions that were only used by
IEEE11hbMgrRxAction.

This allows to fix several warnings reported by sparse.

Signed-off-by: Guillaume Clement <gclement@baobob.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>