Remove Copy trait bound from dyn scalar kernels

[matthewmturner]

Which issue does this PR close?

No existing issue.

Rationale for this change

In the context of apache/datafusion#1685 I am trying to use datafusions ScalarValue with the dyn scalar kernels. We now use the ToPrimitive trait for the dyn scalar kernels and I am looking to implement that on ScalarValue as well. While testing that locally the last issue i came across was ScalarValue not implementing Copy which the dyn scalar kernels require. I tried removing that constraint locally and had no issues compiling / testing / linting so im thinking the constraint isnt needed.

@alamb FYI.

What changes are included in this PR?

Removing Copy trait requirement on the dyn scalar kernels.

Are there any user-facing changes?

[codecov-commenter]

Codecov Report

Merging #1243 (2af8e90) into master (731e132) will decrease coverage by 0.00%.
The diff coverage is n/a.

❗ Current head 2af8e90 differs from pull request most recent head 6d657bb. Consider uploading reports for the commit 6d657bb to get more accurate results

@@            Coverage Diff             @@
##           master    #1243      +/-   ##
==========================================
- Coverage   82.96%   82.95%   -0.01%     
==========================================
  Files         178      178              
  Lines       51522    51522              
==========================================
- Hits        42743    42742       -1     
- Misses       8779     8780       +1     

Impacted Files	Coverage Δ
arrow/src/compute/kernels/comparison.rs	91.70% <ø> (ø)
parquet_derive/src/parquet_field.rs	65.98% <0.00%> (-0.23%)	⬇️
arrow/src/array/transform/mod.rs	84.64% <0.00%> (-0.13%)	⬇️
arrow/src/datatypes/datatype.rs	66.80% <0.00%> (+0.42%)	⬆️

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[alamb]

Nice find @matthewmturner 👍