Improve Tests of UnnecesaryLet

[BraisGabin]

I know that the diff is a bit big but the first commit just moved a test up and rename other ones to keep the number. And the second moves two tests outside the context of tests related with deconstructing arguments.

[codecov]

Codecov Report

Merging #4282 (5b2e3e5) into main (c66b8d6) will not change coverage.
The diff coverage is 100.00%.

❗ Current head 5b2e3e5 differs from pull request most recent head 6997db0. Consider uploading reports for the commit 6997db0 to get more accurate results

@@            Coverage Diff            @@
##               main    #4282   +/-   ##
=========================================
  Coverage     84.22%   84.22%           
  Complexity     3258     3258           
=========================================
  Files           472      472           
  Lines         10309    10309           
  Branches       1820     1820           
=========================================
  Hits           8683     8683           
  Misses          666      666           
  Partials        960      960           

Impacted Files	Coverage Δ
...ab/arturbosch/detekt/rules/style/UnnecessaryLet.kt	80.39% <100.00%> (ø)

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