Remove left over dev/README.md file from arrow/arrow-rs split

[alamb]

Minor cleanup: I noticed a readme file that is outdated

The dev info is included in https://github.com/apache/arrow-rs/blob/master/CONTRIBUTING.md

[codecov-commenter]

Codecov Report

Merging #1162 (76df6bc) into master (884c6a6) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1162   +/-   ##
=======================================
  Coverage   82.55%   82.55%           
=======================================
  Files         173      173           
  Lines       50673    50673           
=======================================
+ Hits        41833    41834    +1     
+ Misses       8840     8839    -1     

Impacted Files	Coverage Δ
arrow/src/array/transform/mod.rs	85.56% <0.00%> (-0.14%)	⬇️
parquet_derive/src/parquet_field.rs	66.43% <0.00%> (+0.45%)	⬆️

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