[clang][APINotes] Fix -Wunused-function warning (NFC)

GCC warning:
```
/llvm-project/clang/lib/APINotes/APINotesYAMLCompiler.cpp:574:23: warning: ‘void {anonymous}::Module::dump()’ defined but not used [-Wunused-function]
  574 | LLVM_DUMP_METHOD void Module::dump() {
      |                       ^~~~~~
```