xrCommon/xr_string.h: Fix for incorrect hash function, it's also disabled on Windows now

Слиты xottab-duty запросил слияние github/fork/ShokerStlk/pr_xd_dev_6 в xd_dev

Created by: ShokerStlk

  1. Original one was calculating hash for pointer, not string itself. So it's was almost always fail to compare two strings by it's hash.
  2. It's not needed for Windows - it has it's own hash implementation in VC++ Redist