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MINOR: [C++] Remove std::move when calling ProcessEmit and ProcessExtensionEmit (#34777)

### Rationale for this change
I noticed a few places in relation_internal.cc that std::move is used incorrectly. 

### What changes are included in this PR?
* Currently, `std::move` is used when passing arguments to `ProcessEmit` and `ProcessExtensionEmit`, however these two methods takes in const reference and therefore the `std::move` is not needed.
* (orthogonal) Removed unneeded `FromProto` from header

### Are these changes tested?
With existing tests

### Are there any user-facing changes?
No

Authored-by: Li Jin <ice.xelloss@gmail.com>
Signed-off-by: Weston Pace <weston.pace@gmail.com>