Assert on correct registeration of outputs index

Assert on correct registeration of outputs index

We remove test_no_failure_dust_htlc_local_commitment from our test
framework as this test deliberately throwing junk transaction in
our monitoring parsing code is hitting new assertions.

This test was added in #333, but it sounds as an oversight as the
correctness intention of this test (i.e verifying lack of dust
HTLCs canceling back in case of junk commitment transaction) doesn't
currently break.