Remove stale comment. NFC (#16934)

The stderr redirection was removed in #9795 but not the comment.

Author: sbc100

tools/building.py

@@ -1294,7 +1294,6 @@ def handle_final_wasm_symbols(wasm_file, symbols_file, debug_info):
   else:
     # suppress the wasm-opt warning regarding "no output file specified"
     args += ['--quiet']
-  # ignore stderr because if wasm-opt is run without a -o it will warn
   output = run_wasm_opt(wasm_file, args=args, stdout=PIPE)
   if symbols_file:
     utils.write_file(symbols_file, output)