[llvm-debuginfod-find] Fix a warning

This patch fixes:

  llvm/tools/llvm-debuginfod-find/llvm-debuginfod-find.cpp:70:19:
  error: unused variable 'ToolName' [-Werror,-Wunused-variable]

Author: kazutakahirata

llvm/tools/llvm-debuginfod-find/llvm-debuginfod-find.cpp

@@ -67,7 +67,6 @@ static std::vector<std::string> DebugFileDirectory;
 
 static void parseArgs(int argc, char **argv) {
   DebuginfodFindOptTable Tbl;
-  llvm::StringRef ToolName = argv[0];
   llvm::BumpPtrAllocator A;
   llvm::StringSaver Saver{A};
   opt::InputArgList Args =