remove: GitHub Actions v1 workflow setting

.github/main.workflow

@@ -1,9 +0,0 @@
-workflow "Main workflow" {
-  on = "push"
-  resolves = ["docker-build"]
-}
-
-action "docker-build" {
-  uses = "actions/docker/cli@master"
-  args = "build -t peaceiris/actions-gh-deploy ."
-}