Revert "Add disk_space() to llvm::fs"

This reverts commit r265074 and r265068.
Breaks windows build

From: Mehdi Amini <mehdi.amini@apple.com>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@265080 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed