Remove unsupported oldrel CI jobs

Author: marlycormar

.github/workflows/R-CMD-check.yaml

@@ -26,15 +26,11 @@ jobs:
           - {os: macos-latest,   r: 'release'}
 
           - {os: windows-latest, r: 'release'}
-          # use 4.0 or 4.1 to check with rtools40's older compiler
-          - {os: windows-latest, r: 'oldrel-4'}
 
           - {os: ubuntu-latest,  r: 'devel', http-user-agent: 'release'}
           - {os: ubuntu-latest,  r: 'release'}
           - {os: ubuntu-latest,  r: 'oldrel-1'}
           - {os: ubuntu-latest,  r: 'oldrel-2'}
-          - {os: ubuntu-latest,  r: 'oldrel-3'}
-          - {os: ubuntu-latest,  r: 'oldrel-4'}
 
     env:
       GITHUB_PAT: ${{ secrets.GITHUB_TOKEN }}