minor #15809 Remove Sphinx build and SymfonyCloud deployment (javiereguiluz)

This PR was merged into the 4.4 branch.

Discussion
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Remove Sphinx build and SymfonyCloud deployment

As discussed internally in the Symfony Docs Team (`@wouterj`, `@xabbuh`, `@weaverryan`, `@OskarStark`) and as discussed with `@fabpot` too, we're removing:

(1) Doc build deployment on SymfonyCloud. Not needed for most contributors because we now have several linters that will alert you about mistakes. Besides, we'll soon switch to a PHP-only solution to build docs, so it'll be trivial to set it up locally (vs the old Sphinx/Python-based or Docker-based doc build which was cumbersome)

(2) The Sphinx-based build on GitHub actions, for the reasons mentioned above: we're about to switch to PHP-only doc building (it's already working locally, but we need to improve/refactor some things).

Commits
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0652757 Remove Sphinx build and SymfonyCloud deployment

Author: javiereguiluz

.github/workflows/ci.yaml

@@ -9,32 +9,6 @@ on:
             - 'github-comments'
 
 jobs:
-    sphinx-build:
-        name: Build (Sphinx)
-
-        runs-on: ubuntu-latest
-
-        container: python:3.7-alpine
-
-        steps:
-            -   name: "Checkout"
-                uses: actions/checkout@v2
-
-            -   name: "Display Python version"
-                run: python -c "import sys; print(sys.version)"
-
-            -   name: "Install Sphinx"
-                run: pip install --user sphinx
-
-            -   name: "Install dependencies"
-                run: apk add --no-cache git make
-
-            -   name: "Install custom requirements via pip"
-                run: pip install -r _build/.requirements.txt
-
-            -   name: "Build documentation"
-                run: make -C _build SPHINXOPTS="-nqW -j auto" html
-
     symfony-docs-builder-build:
         name: Build (symfony-tools/docs-builder)