[clang-tools-extra] [clang-tidy][NFC] Refactor `modernize-use-trailing-return-type-check` check code and tests (PR #140759)

[Nicolas van Kempen via cfe-commits]

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@@ -39,23 +38,6 @@ class UseTrailingReturnTypeCheck : public ClangTidyCheck {
 
 private:
   Preprocessor *PP = nullptr;
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nicovank wrote:

Is this field still needed now?

https://github.com/llvm/llvm-project/pull/140759