GH-45744: [C++] Remove deprecated GetNextSegment

[AlenkaF]

Rationale for this change

GetNextSegment has been deprecated in 18.0.0 and can now be removed.

What changes are included in this PR?

GetNextSegment and related code is removed from compute/row/grouper.cc/.h.

Are these changes tested?

The existing tests should pass.

Are there any user-facing changes?

GetNextSegment is removed in favour of GetSegment

• GitHub Issue: [C++] Remove deprecated GetNextSegment #45744

[zanmato1984]

LGTM with only one nit.

[zanmato1984]

@github-actions crossbow submit -g cpp

[github-actions]

<class 'requests.exceptions.ConnectionError'>: A connection-level exception occurred: ('Connection aborted.', RemoteDisconnected('Remote end closed connection without response'))
The Archery job run can be found at: https://github.com/apache/arrow/actions/runs/13805951286

[zanmato1984]

@github-actions crossbow submit -g cpp

[github-actions]

Revision: 23f880b

Submitted crossbow builds: ursacomputing/crossbow @ actions-23fca30928

Task	Status
example-cpp-minimal-build-static
example-cpp-minimal-build-static-system-dependency
example-cpp-tutorial
test-alpine-linux-cpp
test-build-cpp-fuzz
test-conda-cpp
test-conda-cpp-meson
test-conda-cpp-valgrind
test-cuda-cpp-ubuntu-22.04-cuda-11.7.1
test-debian-12-cpp-amd64
test-debian-12-cpp-i386
test-fedora-39-cpp
test-ubuntu-22.04-cpp
test-ubuntu-22.04-cpp-20
test-ubuntu-22.04-cpp-bundled
test-ubuntu-22.04-cpp-emscripten
test-ubuntu-22.04-cpp-no-threading
test-ubuntu-24.04-cpp
test-ubuntu-24.04-cpp-bundled-offline
test-ubuntu-24.04-cpp-gcc-13-bundled
test-ubuntu-24.04-cpp-gcc-14
test-ubuntu-24.04-cpp-minimal-with-formats
test-ubuntu-24.04-cpp-thread-sanitizer

[zanmato1984]

CI is good. I'm merging. Thank you @AlenkaF !

[conbench-apache-arrow]

After merging your PR, Conbench analyzed the 4 benchmarking runs that have been run so far on merge-commit 4291dad.

There were no benchmark performance regressions. 🎉

The full Conbench report has more details. It also includes information about 7 possible false positives for unstable benchmarks that are known to sometimes produce them.