refactor: make sum_distinct not to have update and merge

[Weijun-H]

Which issue does this PR close?

Parts #1598

Rationale for this change

What changes are included in this PR?

Are these changes tested?

Are there any user-facing changes?

[jimexist]

are unit tests expected to be updated?

[alamb]

are unit tests expected to be updated?

I don't think so -- this is just a small code refactor to avoid calling a backwards compatibility function, I believe

[ursabot]

Benchmark runs are scheduled for baseline = 132ae42 and contender = 8d195a8. 8d195a8 is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ec2-t3-xlarge-us-east-2] ec2-t3-xlarge-us-east-2
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on test-mac-arm] test-mac-arm
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ursa-i9-9960x] ursa-i9-9960x
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ursa-thinkcentre-m75q] ursa-thinkcentre-m75q
Buildkite builds:
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python, R. Runs only benchmarks with cloud = True
test-mac-arm: Supported benchmark langs: C++, Python, R
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java