Merge from Widevine repo of http://go/wvgerrit/57720
Now that we have oemcrypto mock split into reference and testbed code, it is
time to remove the part of testbed that is an exact copy of the reference code
and just use the reference code.
Test: unit tests
Bug: 76393338
Change-Id: I3831a3f0118221c21ff1c28e6b6101b27b889012