Drop aarch64-apple-darwin build xcode+sdk lines.

Xcode 12.2 is likely out of date, and it is breaking PR builds since
the latest mac image bumped to 13.0. Xcode 13.0 uses SDK 11.3 by
default, so we shouldn't need to specify the SDK any longer either,
and not specifying the precise versions ought to be less fragile.

Author: wcarss

.github/workflows/macos-builds-on-all.yaml

@@ -78,13 +78,6 @@ jobs:
 
           # Can't run tests: cross-compiling
           echo "SKIP_TESTS=yes" >> $GITHUB_ENV
-
-          # Use the beta compiler
-          sudo xcode-select -s /Applications/Xcode_12.2.app/Contents/Developer/
-
-          # Set SDK environment variables
-          echo "SDKROOT=$(xcrun -sdk macosx11.0 --show-sdk-path)" >> $GITHUB_ENV
-          echo "MACOSX_DEPLOYMENT_TARGET=$(xcrun -sdk macosx11.0 --show-sdk-platform-version)" >> $GITHUB_ENV
         if: matrix.target == 'aarch64-apple-darwin'
       - name: Ensure we have our goal target installed
         run: |

ci/actions-templates/macos-builds-template.yaml

@@ -78,13 +78,6 @@ jobs:
 
           # Can't run tests: cross-compiling
           echo "SKIP_TESTS=yes" >> $GITHUB_ENV
-
-          # Use the beta compiler
-          sudo xcode-select -s /Applications/Xcode_12.2.app/Contents/Developer/
-
-          # Set SDK environment variables
-          echo "SDKROOT=$(xcrun -sdk macosx11.0 --show-sdk-path)" >> $GITHUB_ENV
-          echo "MACOSX_DEPLOYMENT_TARGET=$(xcrun -sdk macosx11.0 --show-sdk-platform-version)" >> $GITHUB_ENV
         if: matrix.target == 'aarch64-apple-darwin'
       - name: Ensure we have our goal target installed
         run: |