UnrestrictedSessionRunner should not behave differently in Unit Test

Since NXP-14118 there is an extra session.save() in test mode for already unrestricted session.

The session.save reads session invalidations from other transactions which makes unit test behave very differently than Nuxeo instance. This extra code should be removed.

Note that the low level session (SQLSession/DBSSession) is shared by all high level session in the same transaction. It is not necessary to call session.save to load invalidation from other session in the same transaction.