remove obsolete circleci config

tests/pendulum/.circleci/config.yml

@@ -1,73 +0,0 @@
-
-version: 2.1
-
-workflows:
-  version: 2
-
-  workflow:
-    jobs:
-      - Linux
-      - MacOS
-
-jobs:
-
-  Linux:
-    docker:
-      - image: nixos/nix
-
-    steps:
-
-      - checkout
-
-      - run:
-          name: Build
-          command: |
-            nix-shell --run "python --version"
-
-  MacOS:
-    macos:
-      xcode: 11.4.1
-
-    steps:
-
-      - run:
-          name: Install Nix
-          command: |
-            # Nix installation adapted from
-            # https://github.com/cachix/install-nix-action/blob/master/lib/install-nix.sh
-            set -euo pipefail
-
-            # This paragraph's steps are copied from
-            # https://github.com/NixOS/nix/blob/26fcab53e05ce66f5533f0f07ed13d727a891c8d/scripts/create-darwin-volume.sh
-            echo nix | sudo tee -a /etc/synthetic.conf
-            /System/Library/Filesystems/apfs.fs/Contents/Resources/apfs.util -B
-            disk=$(diskutil info -plist / | xpath "/plist/dict/key[text()='ParentWholeDisk']/following-sibling::string[1]/text()" 2>/dev/null)
-            sudo diskutil apfs addVolume "$disk" APFS 'Nix Store' -mountpoint /nix
-
-            # Can't be bothered to get a daemon installation to work, so we'll
-            # just do a single-user installation instead.
-            sudo diskutil enableOwnership /nix
-            sudo chown -R "$(whoami)" /nix
-
-            sh <(curl -sS --retry 5 --retry-connrefused -L https://nixos.org/nix/install) </dev/null --no-channel-add
-
-            # Disable spotlight indexing of /nix to speed up performance
-            sudo mdutil -i off /nix
-
-            sudo mkdir -p /etc/nix
-            echo "max-jobs = auto" | sudo tee -a /etc/nix/nix.conf
-
-            # macOS needs certificates hints
-            cert_file=/nix/var/nix/profiles/per-user/$(whoami)/profile/etc/ssl/certs/ca-bundle.crt
-            echo "export NIX_SSL_CERT_FILE=$cert_file" >> $BASH_ENV
-
-            # Set paths
-            echo "export PATH=/nix/var/nix/profiles/per-user/$(whoami)/profile/bin:\$PATH" >> $BASH_ENV
-
-      - checkout
-
-      - run:
-          name: Build
-          command: |
-            nix-shell --run "python --version"
-