Remove testUnknownSourcesByDefaultTest

This was expected to be removed by merging in the changes
from Froyo. However, since the change originated in GB,
the cherry-picking into Froyo and removing it in Froyo
ended up as a no-op when merging the removal back into GB.
Thus, remove this again!

Change-Id: I95ff719a1ce6b276e00d33e3286bd49c2255759d