chore: remove Sourcehut CI manifest

Migrated to git.swaits.com; Sourcehut builds no longer run.

.build.yml

@@ -1,27 +0,0 @@
-image: alpine/edge
-packages:
-  - git
-
-secrets:
-  - 88cce185-d2ec-4573-9546-e33f36f79bbf
-
-environment:
-  # repo and user names on both sr.ht and github
-  REPO: universal-clipboard.nvim
-  USER: swaits
-
-tasks:
-  - fetch-all-branches: |
-      cd "$HOME/$REPO"
-      git fetch origin '+refs/heads/*:refs/heads/*' '+refs/tags/*:refs/tags/*' --prune
-
-  - get-github-public-key: |
-      ssh-keyscan -t rsa github.com >> "$HOME/.ssh/known_hosts"
-
-  - add-github-remote: |
-      cd "$HOME/$REPO"
-      git remote add github "git@github.com:$USER/$REPO.git"
-
-  - mirror-to-github: |
-      cd "$HOME/$REPO"
-      git push --mirror github