remove 1/2 in branch AFS: closes #2925

[petrelharp]

Note also the (fairly cursory) tests that (a) fold(branch AFS) == (branch AFS, unpolarised) and (b) the same is true for site AFS with infinite-sites.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 89.63%. Comparing base (308f67e) to head (2175169).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2933 +/- ## ======================================= Coverage 89.63% 89.63% ======================================= Files 29 29 Lines 30170 30174 +4 Branches 5864 5873 +9 ======================================= + Hits 27042 27046 +4 Misses 1789 1789 Partials 1339 1339 ``` | [Flag](https://app.codecov.io/gh/tskit-dev/tskit/pull/2933/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tskit-dev) | Coverage Δ | | |---|---|---| | [c-tests](https://app.codecov.io/gh/tskit-dev/tskit/pull/2933/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tskit-dev) | `86.20% <ø> (+<0.01%)` | :arrow_up: | | [lwt-tests](https://app.codecov.io/gh/tskit-dev/tskit/pull/2933/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tskit-dev) | `80.78% <ø> (ø)` | | | [python-c-tests](https://app.codecov.io/gh/tskit-dev/tskit/pull/2933/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tskit-dev) | `88.72% <ø> (+<0.01%)` | :arrow_up: | | [python-tests](https://app.codecov.io/gh/tskit-dev/tskit/pull/2933/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tskit-dev) | `99.03% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tskit-dev#carryforward-flags-in-the-pull-request-comment) to find out more. | [Files](https://app.codecov.io/gh/tskit-dev/tskit/pull/2933?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tskit-dev) | Coverage Δ | | |---|---|---| | [c/tskit/trees.c](https://app.codecov.io/gh/tskit-dev/tskit/pull/2933?src=pr&el=tree&filepath=c%2Ftskit%2Ftrees.c&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tskit-dev#diff-Yy90c2tpdC90cmVlcy5j) | `90.42% <ø> (-0.01%)` | :arrow_down: | ... and [2 files with indirect coverage changes](https://app.codecov.io/gh/tskit-dev/tskit/pull/2933/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tskit-dev)

[petrelharp]

I think this is ready to go!

[jeromekelleher]

LGTM - we should update the CHANGELOG though, or we'll forget.

[petrelharp]

Done. I see codecov is still weird, but I think it's safe to merge this.

[jeromekelleher]

Yep, happy to merge.

What's going on with the cache thing in MacOS @benjeffery?

[petrelharp]

It seems to be lowering coverage slightly because it's just reduced the denominator. I'll let you hit merge, since I'm not sure if merging PRs where CI failed has undesired effects?

[benjeffery]

Looks like something has changed in the osx base image? Will look into it.

[benjeffery]

Done. I see codecov is still weird, but I think it's safe to merge this.

Note that https://github.com/tskit-dev/tskit/issues/2931 is ongoing.

[jeromekelleher]

Let's try rebasing this again when #2935 and #2937 are through - hopefully we'll start getting reliable green-lights from CI again and we can start getting PRs through more easily.

[benjeffery]

@mergifyio rebase

[mergify[bot]]

rebase

✅ Branch has been successfully rebased