GH-45605: [R][C++] Fix identifier ... preceded by whitespace warnings (…

…#45606)

### Rationale for this change

Fix warnings, pass on CRAN

### What changes are included in this PR?

Removing some whitespace

### Are these changes tested?

Yes

### Are there any user-facing changes?

No, other than being releasable on CRAN

* GitHub Issue: #45605

Authored-by: Jonathan Keane <jkeane@gmail.com>
Signed-off-by: Bryce Mecum <petridish@gmail.com>

[Release] Apache Arrow Release 19.0.1

[Release] Apache Arrow Release 19.0.0 RC1

[Release] Apache Arrow Release 19.01 RC0

MINOR: [Release] Update .deb/.rpm changelogs for 19.0.0

[Release] Apache Arrow Release 19.0.0

[Release] Apache Arrow Release 19.0.0 RC0

[Release] Apache Arrow Release 18.1.0

[Release] Apache Arrow Release 18.1.0 RC2

[Release] Apache Arrow Release 18.1.0 RC1