Don't redundantly delete temporary directories in RSCriptExecutor.

[cmnbroad]

Fixes #5893.

[codecov-io]

Codecov Report

Merging #5894 into master will increase coverage by 0.008%.
The diff coverage is n/a.

@@              Coverage Diff               @@
##              master    #5894       +/-   ##
==============================================
+ Coverage     86.843%   86.85%   +0.008%     
+ Complexity     32321    32319        -2     
==============================================
  Files           1991     1991               
  Lines         149308   149302        -6     
  Branches       16486    16485        -1     
==============================================
+ Hits          129663   129669        +6     
+ Misses         13630    13621        -9     
+ Partials        6015     6012        -3

Impacted Files	Coverage Δ	Complexity Δ
...dinstitute/hellbender/utils/R/RScriptExecutor.java	89.231% <ø> (+0.498%)	18 <0> (-2)	⬇️
...lotypecaller/readthreading/ReadThreadingGraph.java	88.971% <0%> (+0.245%)	159% <0%> (ø)	⬇️
...nder/utils/runtime/StreamingProcessController.java	67.773% <0%> (+0.474%)	33% <0%> (ø)	⬇️
...e/hellbender/engine/spark/SparkContextFactory.java	73.973% <0%> (+2.74%)	11% <0%> (ø)	⬇️
...utils/smithwaterman/SmithWatermanIntelAligner.java	90% <0%> (+10%)	3% <0%> (ø)	⬇️
...nder/utils/smithwaterman/SmithWatermanAligner.java	81.818% <0%> (+13.636%)	2% <0%> (ø)	⬇️
...ithwaterman/SmithWatermanIntelAlignerUnitTest.java	90% <0%> (+30%)	2% <0%> (ø)	⬇️