GH-36610: [CI][C++] Don't enable ARROW_ACERO by default (#36611)

### Rationale for this change

Because it's not a required component.

### What changes are included in this PR?

Use `OFF` by default.

### Are these changes tested?

Yes.

### Are there any user-facing changes?

No.
* Closes: #36610

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

ci/scripts/cpp_build.sh

@@ -83,7 +83,7 @@ pushd ${build_dir}
 
 cmake \
   -Dabsl_SOURCE=${absl_SOURCE:-} \
-  -DARROW_ACERO=${ARROW_ACERO:-ON} \
+  -DARROW_ACERO=${ARROW_ACERO:-OFF} \
   -DARROW_AZURE=${ARROW_AZURE:-OFF} \
   -DARROW_BOOST_USE_SHARED=${ARROW_BOOST_USE_SHARED:-ON} \
   -DARROW_BUILD_BENCHMARKS_REFERENCE=${ARROW_BUILD_BENCHMARKS:-OFF} \