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GH-41478: [C++] Clean up more redundant move warnings (#41487)



### Rationale for this change

Minor warning cleanup for downstream libraries trying to get warning-free builds

### What changes are included in this PR?

Removed redundant std::move from return statements

### Are these changes tested?

Builds cleanly

### Are there any user-facing changes?

No

* GitHub Issue: #41478

Authored-by: Will Ayd <william.ayd@icloud.com>
Signed-off-by: Benjamin Kietzman <bengilgit@gmail.com>