Remove IT_LITERAL & LET_LITERAL

[3flex]

LET_LITERAL was unused.

IT_LITERAL is provided by StandardNames.IMPLICIT_LAMBDA_PARAMETER_NAME which has resulted in more descriptive code IMHO. There was one usage which I've replaced with string "it" because the rule is literally checking for "`it`-started expressions" so I think this is reasonable.

[detekt-ci]

	Warnings
⚠️	It looks like this PR contains functional changes without a corresponding test.

Generated by 🚫 dangerJS against ac60908

[codecov]

Codecov Report

Attention: Patch coverage is 87.50000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 84.76%. Comparing base (1b00a0c) to head (ac60908).
Report is 1 commits behind head on main.

Files	Patch %	Lines
.../arturbosch/detekt/rules/style/AlsoCouldBeApply.kt	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #7310   +/-   ##
=========================================
  Coverage     84.76%   84.76%           
  Complexity     3992     3992           
=========================================
  Files           578      578           
  Lines         12026    12026           
  Branches       2477     2477           
=========================================
  Hits          10194    10194           
  Misses          606      606           
  Partials       1226     1226           

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[BraisGabin]

Approved because this is clearly better than before but I would use "it" directly. At least for me IMPLICIT_LAMBDA_PARAMETER_NAME is more complex than "it".

[3flex]

I think it's better to use type safe values, and using a Name instead of a plain string assists with that. IMPLICIT_LAMBDA_PARAMETER_NAME is awkward but it's descriptive. Maybe just my preference but I think we should promote type safety in our rule implementations.

[BraisGabin]

Oh, I thought that it was just a plain string too. I'm still not 100% on board but it's good for me. This PR reduces complexity on our public api and that's the important point.

[cortinico]

At least for me IMPLICIT_LAMBDA_PARAMETER_NAME is more complex than "it".

If so, we could have our own internal field that maps to IMPLICIT_LAMBDA_PARAMETER_NAME