gcm: remove cask

Remove GCM cask per Homebrew's instructions on tap migrations [1]. Note
that this should be merged at the same time [2] is merged.

[1]: https://docs.brew.sh/Migrating-A-Formula-To-A-Tap
[2]: https://github.com/Homebrew/homebrew-cask/pull/152552

Casks/git-credential-manager-core.rb

@@ -1,20 +0,0 @@
-cask 'git-credential-manager-core' do
-  arch = Hardware::CPU.intel? ? "x64" : "arm64"
-  name 'Git Credential Manager'
-  homepage 'https://aka.ms/gcm'
-
-  version "2.3.0"
-  if Hardware::CPU.intel?
-    sha256 '2c835e24eb5223ef190c528f12a7d7054b8ca143f7399ab23f61c68c0b8e029b'
-  else
-    sha256 '8acfa913307140c06ec9b2692f9abfef32ecde4c83634d728597a94d34e0e773'
-  end
-
-  url "https://github.com/GitCredentialManager/git-credential-manager/releases/download/v#{version.major_minor_patch}/gcm-osx-#{arch}-#{version.major_minor_patch}.pkg"
-  pkg "gcm-osx-#{arch}-#{version}.pkg", allow_untrusted: true
-  uninstall script: {
-                      executable: "/usr/local/share/gcm-core/uninstall.sh",
-                      sudo:       true,
-                    },
-            pkgutil: 'com.microsoft.GitCredentialManager'
-end

tap_migrations.json

@@ -0,0 +1,3 @@
+{
+    "git-credential-manager-core": "homebrew/cask/git-credential-manager"
+}