Remove specialized PartialQuickSort{<:Integer} method (#36896)
This specialized method is actually considerably slower than the one that also
works for `PartialQuickSort{<:OrdinalRange}`. It had been removed before in
9e8fcd3 due to an inference issue, and reintroduced by c41d5a3 (#31632) once
that issue got fixed, but apparently without benchmarks. It turns out that saving
one comparison per iteration isn't worth it. The gain is especially large when
looking for a value among the largest in the array, as the specialized method always
sorted all values lower than the requested one.
