bindexplib: remove stray debugging output when using llvm-nm

Remove a debugging message left by commit c856d4556b (bindexplib:
supporting llvm bitcode formats using llvm-nm, 2019-08-13,
v3.16.0-rc1~161^2~1).

Source/cmcmd.cxx

@@ -754,7 +754,6 @@ int cmcmd::ExecuteCMakeCommand(std::vector<std::string> const& args,
         std::string const& a = args[4];
         if (cmHasLiteralPrefix(a, "--nm=")) {
           deffile.SetNmPath(a.substr(5));
-          std::cerr << a.substr(5) << "\n";
         } else {
           std::cerr << "unknown argument: " << a << "\n";
         }