minor: remove test code that's in the arrow library now

[kmitchener]

Which issue does this PR close?

Closes #.

Rationale for this change

Handling of the FixedSizeList datatype is in the arrow array_value_to_string() function, it doesn't need special case handling in DF test code anymore.

What changes are included in this PR?

Are there any user-facing changes?

[codecov-commenter]

Codecov Report

Merging #3206 (928c10b) into master (929eb6d) will increase coverage by 0.00%.
The diff coverage is n/a.

❗ Current head 928c10b differs from pull request most recent head 19e16f5. Consider uploading reports for the commit 19e16f5 to get more accurate results

@@           Coverage Diff           @@
##           master    #3206   +/-   ##
=======================================
  Coverage   85.87%   85.88%           
=======================================
  Files         291      291           
  Lines       52885    52879    -6     
=======================================
- Hits        45415    45413    -2     
+ Misses       7470     7466    -4     

Impacted Files	Coverage Δ
datafusion/core/tests/sql/mod.rs	97.77% <ø> (+0.82%)	⬆️
datafusion/expr/src/logical_plan/plan.rs	77.60% <0.00%> (-0.18%)	⬇️

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[alamb]

Thanks @kmitchener !

[ursabot]

Benchmark runs are scheduled for baseline = 3c911ff and contender = a52dbb0. a52dbb0 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