copies: stop attempt to avoid extra dict copies around branching In the python code, we attempt to avoid unnecessary dict copies when gathering copy information. However that logic is wobbly and I keep running into case where independent branches affects each others. With the current code we can't ensure we are the only "user" of dict when dealing with merge. This caused havoc in the next series on tests I am about to introduce. So for now I am disabling the faulty optimisation. I believe we will need a dedicated overlay to deal with the "copy on write logic" to have something correct. I am also hoping to find time to build dedicated test case for this category of problem instead of relying on side effect in other tests. However for now I am focussing on another issue. Differential Revision: https://phab.mercurial-scm.org/D9608