arrow

MINOR: [R] Remove trailing whitespace in configure (#36690)

### What changes are included in this PR?

Fixes trailing whitespace in configure so that it's easier to get a clean commit history on the file.

### Are these changes tested?

No.

### Are there any user-facing changes?

No.

Authored-by: Dewey Dunnington <dewey@voltrondata.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>