minor: remove unneeded files from project root

[kmitchener]

Which issue does this PR close?

Closes #.

Rationale for this change

Learning the project, the code, the repo -- the less to wade through, the better. Better to clean up files that aren't used.

What changes are included in this PR?

I'm fairly confident none of these files are used. No references in the project and latest updates are usually quite old. I believe they're leftovers from some previous migration.

Are there any user-facing changes?

No

[codecov-commenter]

Codecov Report

Merging #2863 (0f82a8c) into master (a2da720) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2863   +/-   ##
=======================================
  Coverage   85.24%   85.25%           
=======================================
  Files         275      275           
  Lines       49002    49001    -1     
=======================================
+ Hits        41773    41776    +3     
+ Misses       7229     7225    -4     

Impacted Files	Coverage Δ
datafusion/core/src/execution/memory_manager.rs	69.95% <0.00%> (-0.31%)	⬇️
datafusion/expr/src/logical_plan/plan.rs	74.70% <0.00%> (+0.39%)	⬆️
datafusion/sql/src/utils.rs	51.95% <0.00%> (+0.40%)	⬆️
datafusion/core/src/physical_plan/metrics/value.rs	87.43% <0.00%> (+0.50%)	⬆️

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[xudong963]

Thanks @kmitchener