Removes old ppa for opam (#10161)

.github/workflows/main.yml

@@ -272,7 +272,6 @@ jobs:
       - name: Install dependencies
         run: |
           set -ex
-          sudo add-apt-repository ppa:avsm/ppa -y # provides OPAM 2
           sudo add-apt-repository ppa:haxe/ocaml -y # provides newer version of mbedtls
           sudo apt-get update -qqy
           sudo apt-get install -qqy ocaml-nox camlp5 opam libpcre3-dev zlib1g-dev libgtk2.0-dev libmbedtls-dev ninja-build libstring-shellquote-perl