Revert "detect-virt: also detect "microsoft" as WSL"

Revert "detect-virt: also detect "microsoft" as WSL"

WSL2 will soon (TM) include the "WSL2" string in /proc/sys/kernel/osrelease
so the workaround will no longer be necessary.
We have several different cloud images which do include the "microsoft"
string already, which would break this detection. They are for internal
usage at the moment, but the userspace side can come from all over the
place so it would be quite hard to track and downstream-patch to avoid
breakages.

This reverts commit a2f838d59075a49b012f9b7056664f7ffeed44d2.