Enable the biometric verification feature by default

Test: atest BinaryTransparencyServiceTest
Test: On a flash build (with the flag value being null), manually check
      if the default value takes effective and the feature is enabled
      properly by running "m statsd_testdrive && statsd_testdrive 587"
Bug: 266484331
Change-Id: I8c9604995b838790b7efe56cdbc409dadc462921