fixup: drop x86_64-darwin devshell (#189)

Author: cole-h

.github/workflows/flakehub-cache.yml

@@ -17,8 +17,6 @@ jobs:
         systems:
           - nix-system: aarch64-darwin
             runner: macos-latest-xlarge
-          - nix-system: x86_64-darwin
-            runner: macos-latest-xlarge
           - nix-system: x86_64-linux
             runner: UbuntuLatest32Cores128G
     steps: