[clang-tools-extra] [clang-tidy][NFC] Do less unnecessary work in `NoLintDirectiveHandler` (PR #147553)

[Victor Chernyakin via cfe-commits]

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@@ -31,8 +31,6 @@ class NoLintDirectiveHandler {
 public:
   NoLintDirectiveHandler();
   ~NoLintDirectiveHandler();
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localspook wrote:

This check does backflips to keep the definition of `Impl` out of the header, and this is one of those backflips. The destructor must be defined in the `.cpp`, because the destructor of `Impl` (and by proxy, the destructor of `std::unique_ptr<Impl>`) is only visible in the `.cpp`.

https://github.com/llvm/llvm-project/pull/147553