Revert "[flang][runtime] Support all non-ASCII characters in temporary path on Windows"

This reverts commit fd0d8466.

It seems to have broken various flang unit tests on AArch64 Windows platform.

https://lab.llvm.org/buildbot/#/builders/65/builds/9856
https://lab.llvm.org/buildbot/#/builders/120/builds/4883

Differential Revision: https://reviews.llvm.org/D151571