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

GCC warning:
```
/llvm-project/clang/lib/APINotes/APINotesYAMLCompiler.cpp:574:6: warning: ‘void {anonymous}::Module::dump()’ defined but not used [-Wunused-function]
  574 | void Module::dump() {
      |      ^~~~~~
```