[idp saml2] fix removal of sessions during SP intiated logout for the requesting provider
[idp saml2] fix removal of sessions during SP intiated logout for the requesting provider

We must remove all sessions for the given provider in the current
session. Old code removed all sessions for the given provider with the
transmistted session index, forgotting to remove session for old
assertion emitted for the same provider in the same session.

pu239ppy/authentic2,incuna/authentic,incuna/authentic,pu239ppy/authentic2,pu239ppy/authentic2,incuna/authentic,BryceLohr/authentic,incuna/authentic,incuna/authentic,adieu/authentic2,adieu/authentic2,BryceLohr/authentic,BryceLohr/authentic,adieu/authentic2,adieu/authentic2,BryceLohr/authentic,pu239ppy/authentic2