Restrict SAML logout request when new user provisioning is not enabled [#3227114]

Problem/Motivation

When 'Register users (i.e., auto-provisioning)' setting is not enabled, immediately after receiving the SAML response the system initiates SAML logout request that logs out user from other different portal as well (for which SAML was the authentication source).

Issue fork simplesamlphp_auth-3227114

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3227114-restrict-saml-logout changes, plain diff MR !5
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