[NFC] Remove out dated comment for clear-ast-before-backend

The comment is outdated since d0a5f61

Author: ChuanqiXu9

clang/include/clang/Basic/CodeGenOptions.def

@@ -58,7 +58,7 @@ ENUM_CODEGENOPT(FramePointer, FramePointerKind, 2, FramePointerKind::None, Benig
 
 ENUM_CODEGENOPT(ExceptionHandling, ExceptionHandlingKind, 3, ExceptionHandlingKind::None, NotCompatible)
 
-CODEGENOPT(ClearASTBeforeBackend , 1, 0, Benign) ///< Free the AST before running backend code generation. Only works with -disable-free.
+CODEGENOPT(ClearASTBeforeBackend , 1, 0, Benign) ///< Free the AST before running backend code generation.
 CODEGENOPT(DisableFree       , 1, 0, Benign) ///< Don't free memory.
 CODEGENOPT(DiscardValueNames , 1, 0, Benign) ///< Discard Value Names from the IR (LLVMContext flag)
 CODEGENOPT(DisableLLVMPasses , 1, 0, Benign) ///< Don't run any LLVM IR passes to get