conflux: Flag set as in full teardown in the free path

Note that I do not mark the other circuits for close anymore; That was causing a test failure.

Upon further reflection, if this is shutdown, there is no need to mark. If this is not shutdown, it could be dangerous to mark, since we do not know the cause for this.

So leaving out the mark for close seems best, here.

This is only for main to start, since we don't know for sure that this is even the cause. We can backport after another report, or if we get some exercise of this in Shadow or in an 0.4.9 alpha.