For each unwanted dependency removal (ie for each such
branch), search as follows:
* An "unwanted removal commit" is a non-merge commit in the
- history of the source, which unwantedly removes the dep
- from the actual included deps.
+ history of the source, which removes the dep from the
+ actual included deps.
* But the search stops at any point where we would have to
traverse a commit where .topbloke/deps is empty (which
stops us looking into the hitory of non-topbloke-controlled