revset: drop unreachable code

perf: add a benchmark for revrange

test-tags: enable for Windows It turns out that MSYS does have a chmod.exe, but it has no effect. So, the inserted "#if unix-permissions" is somewhat redundant, as the test would pass without it as well: it would simply write the tag cache, despite what the comment says. But I'm actually in favor of inserting the #if, as it makes it clearer what's going on.