Simplify reporting message for IgnoredReturnValue

[cortinico]

Simplifies the error message for IgnoredReturnValue to report only the name of the caller that is affected by the finding. I also added a hasMessage method to our FindingAssert as we happen to have several scenarios where we want to asset the message in the codebase.

Fixes #3052

[codecov]

Codecov Report

Merging #3068 into master will decrease coverage by 0.01%.
The diff coverage is 50.00%.

@@             Coverage Diff              @@
##             master    #3068      +/-   ##
============================================
- Coverage     79.27%   79.26%   -0.02%     
  Complexity     2563     2563              
============================================
  Files           432      432              
  Lines          7725     7726       +1     
  Branches       1468     1469       +1     
============================================
  Hits           6124     6124              
  Misses          816      816              
- Partials        785      786       +1     

Impacted Files	Coverage Δ	Complexity Δ
...arturbosch/detekt/rules/bugs/IgnoredReturnValue.kt	75.51% <50.00%> (-1.58%)	14.00 <0.00> (ø)

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