.github/workflows: delete flaky windows-race.yml

It flakes more often than it runs. It provides no value and builds
failure blindness, making people get used to submitting on red.

Bye.

Change-Id: If5491c70737b4c9851c103733b1855af2a90a9e9
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f