Revert "libstagefright: free mMoovBoxBuffer"

This reverts commit 5e179e6a, it
causes a MAPERR in concurrent/crossed camera accesses (like trying
to record on a camera locked by another process)

Fixes android.hardware.cts.CameraTest#testLockUnlock

Change-Id: I2379dc257fc0d5e610a4142186d3100d5bcea6f6