Minor: clean up aggregates.slt tests

[alamb]

Which issue does this PR close?

Related to #4495

Rationale for this change

There are some out of date errors I noticed while working on #5574

What changes are included in this PR?

uncomment some tests in aggregates.slt and remove TODOs that have been done

Are these changes tested?

Yes they are tests

Are there any user-facing changes?

No

[alamb]

These tests are added in #5574

[alamb]

Added type check per comment

[jackwener]

👍

[jackwener]

I reviewed this PR carefully.
Because this PR isn't complex and this PR may block other PR about agg.slt(or may cause conflict), so I quickly merged it.

Thanks @alamb

[ursabot]

Benchmark runs are scheduled for baseline = 4d07360 and contender = 35a3acf. 35a3acf 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