Revert "algo: Improve InsSort performance by 2% to 34%."

This reverts commit b3dabc46b7828ea0293a5dde4ed084f9dcffb353.

The code was easier to read before the commit and the compiler will eventually
be able to do this kind of optimizations automatically.
algo: Update comments for InsSort and SelSort.
algo: Minor optimization of SelSort.

benchmark                   old ns/op    new ns/op    delta
BenchmarkSelSortRand1e2          7390         7387   -0.04%
BenchmarkSelSortRand1e3        513174       513545   +0.07%
BenchmarkSelSortRand1e4      44713153     44578339   -0.30%
BenchmarkSelSortWorst1e2         6651         6618   -0.50%
BenchmarkSelSortWorst1e3       461730       460462   -0.27%
BenchmarkSelSortWorst1e4     43852149     43854541   +0.01%