Remove outdated comment

Author: DavisVaughan

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

@@ -30,7 +30,6 @@ jobs:
           # Use 3.6 to trigger usage of RTools35
           # - {os: windows-latest, r: '3.6'}
 
-          # Use older ubuntu to maximise backward compatibility
           - {os: ubuntu-latest,   r: 'devel', http-user-agent: 'release'}
           - {os: ubuntu-latest,   r: 'release'}
           - {os: ubuntu-latest,   r: 'oldrel-1'}