Explicitly clear cleanup function on release
Explicitly clear cleanup function on release

std::move is allowed to leave the variable in any valid state, so we
can't rely on it setting it to a state that converts to Boolean false
(which is the attribute on which ~Cleanup relies).
PiperOrigin-RevId: 249538001
Change-Id: Ied14f14e9edfb5cba98777e00ee6d49aad299ca9

google/asylo,google/asylo,google/asylo,google/asylo,google/asylo,google/asylo