ARROW-15656: [C++] [R] Make valgrind builds slightly quicker
ARROW-15656: [C++] [R] Make valgrind builds slightly quicker

It looks like these specific errors have been resolved in other tickets. In the process of isolating the issue, I found that we actually were building arrow twice in the build. So I've repurposed this PR to remove the extraneous build.

Closes #12700 from jonkeane/valgrind-bisect

Authored-by: Jonathan Keane <28d17c45cab2bb8b25bea44a915713e26ce37e1b@gmail.com>
Signed-off-by: Weston Pace <0dd0706858a011bb30a3fd82b71cee4f9094c502@gmail.com>

wesm/arrow,icexelloss/arrow,apache/arrow,icexelloss/arrow,kou/arrow,apache/arrow,icexelloss/arrow,kou/arrow,kou/arrow,wesm/arrow,apache/arrow,icexelloss/arrow,wesm/arrow,wesm/arrow,apache/arrow,kou/arrow,kou/arrow,wesm/arrow,wesm/arrow,apache/arrow,icexelloss/arrow,apache/arrow,kou/arrow,icexelloss/arrow,apache/arrow,kou/arrow,apache/arrow,kou/arrow,wesm/arrow,icexelloss/arrow,wesm/arrow,icexelloss/arrow,wesm/arrow,icexelloss/arrow,kou/arrow,apache/arrow,wesm/arrow,icexelloss/arrow,apache/arrow,apache/arrow,kou/arrow,apache/arrow,apache/arrow,kou/arrow,kou/arrow,kou/arrow,icexelloss/arrow,icexelloss/arrow,icexelloss/arrow,icexelloss/arrow,wesm/arrow,apache/arrow,wesm/arrow,kou/arrow,wesm/arrow,wesm/arrow