chore: remove old web-proxy code

This is no longer used in our infra, and probably should never have
been in this repo anyway

Closes: PluralKit/PluralKit#511

.github/workflows/fly.yml

@@ -1,19 +0,0 @@
-name: Deploy web proxy to Fly.io
-
-on:
-  push:
-    branches: [main]
-    paths:
-      - 'services/web-proxy/**'
-
-env:
-  FLY_API_TOKEN: ${{ secrets.FLY_API_TOKEN }}
-
-jobs:
-  deploy:
-      name: Deploy app
-      runs-on: ubuntu-latest
-      steps:
-        - uses: actions/checkout@v2
-        - uses: superfly/flyctl-actions/setup-flyctl@master
-        - run: (cd services/web-proxy && flyctl deploy)