[R] Remove duplicate setting of S3 flag on macOS #26351
Description
Observed here: autobrew/scripts#3 (comment)
It doesn't hurt anything but might as well clean it up.
Reporter: Neal Richardson / @nealrichardson
Assignee: Neal Richardson / @nealrichardson
PRs and other links:
Note: This issue was originally created as ARROW-10365. Please see the migration documentation for further details.