chore: remove unused legacy .github/actions/action.yml

This monolithic NPM/NuGet/Octopus-deploy composite action is a dead
copy synced in from tooling — it is not referenced by any workflow or
other composite action in this repo. Confirmed via a cross-repo audit
covering the credfeto and funfair-tech orgs (both local `uses:
./.github/actions` and pinned remote `uses: owner/repo/.github/actions@ref`
forms checked).

Prompt: murder it everywhere

Author: credfeto