Currently we can't automatically enforce formatting on tests (see #125637), but
we can at least keep things relatively tidy by occasionally running the
formatter manually.
This was done by temporarily commenting out the `"/tests/"` exclusion in
`rustfmt.toml`, and then running `x fmt tests/coverage` and
`x test coverage --bless`.
These assertions detect situations where a BCB node would have both a physical
counter and one or more in-edge counters/expressions.
For most BCBs that situation would indicate an implementation bug. However,
it's perfectly fine in the case of a BCB having an edge that loops back to
itself.
Given the complexity and risk involved in fixing the assertions, and the fact
that nothing relies on them actually being true, this patch just removes them
instead.
