Revert "Downspeed the read from USB flash during AUM USB unplug test"

This reverts commit c86d18a7.
The problem of low speed bandwidth is kernel crash (APERTIS-6016) which
completely blocking the USB unplug test.

With changes provided in previous commit we provide the binary diff
big enough to catch the proper timing by human and without kernel
crashes.

Signed-off-by: Denis Pynkin <denis.pynkin@collabora.com>