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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>