Temporarily disable cross-compiled Mac platforms

Homebrew recently dropped support for OpenSSL 1.1 because it's
end-of-life. However, our cross-compiled macOS platforms (11 and 12 on
ARM) still depend on OpenSSL.

While we work on hosting our own OpenSSL 1.1 formula (see PA-7103), this
commit disables building on those platforms for now.

ext/build_defaults.yaml

@@ -21,9 +21,7 @@ foss_platforms:
   - el-9-ppc64le
   - fedora-36-x86_64
   - fedora-40-x86_64
-  - osx-11-arm64
   - osx-11-x86_64
-  - osx-12-arm64
   - osx-12-x86_64
   - osx-13-arm64
   - osx-13-x86_64
@@ -118,12 +116,8 @@ platform_repos:
     repo_location: repos/apt/noble
   - name: ubuntu-24.04-aarch64
     repo_location: repos/apt/noble
-  - name: osx-11-arm64
-    repo_location: repos/apple/11/**/arm64/*.dmg
   - name: osx-11-x86_64
     repo_location: repos/apple/11/**/x86_64/*.dmg
-  - name: osx-12-arm64
-    repo_location: repos/apple/12/**/arm64/*.dmg
   - name: osx-12-x86_64
     repo_location: repos/apple/12/**/x86_64/*.dmg
   - name: osx-13-arm64