[FIX] orm.search_read: drop active_test context flag during the read() step

The active_test flag is meant for search(),
but when passed to search_read() it was also
propagated to the read() call.
This has little consequence normally because
read() ignores this flag, but it can have
side-effects when reading x2m fields or
function fields. They are likely to call
search() somewhere downstream, still with
 the propagated active_test flag, while
it should not be applied anymore.

Ultimately dropping this flag could be
done by read() in all cases, but changing
search_read() is less likely to block
exotic cases where the flag was passed
on purpose. Moving it to read() could
be done as a later step.