This CL also removes wait_for_strongbox, which is broken because it
looks only for keymaster implementations, not keymint. But it's also
unnecessary due to reorganization of the way keystore and vold start
up.
Bug: 177729159
Test: boot & VtsAidlKeyMintTargetTest
Change-Id: I6c5210356396b2079e036e94bb909f3a1a31e6c6