[clang] [clang][Lex] Fix conflicting RemoveTopOfLexerStack docs (PR #214679)

[Mariya Podchishchaeva via cfe-commits]

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@@ -1747,7 +1747,7 @@ class Preprocessor {
   /// Pop the current lexer/macro exp off the top of the lexer stack.
   ///
   /// This should only be used in situations where the current state of the
-  /// top-of-stack lexer is known.
+  /// top-of-stack lexer is unknown.
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Fznamznon wrote:

Should we just remove the doc comment from either here or .cpp file to avoid duplication?

https://github.com/llvm/llvm-project/pull/214679