bin/pegjs: Remove detailed instructions from the help text

They don't belong there.

Part of #370.

bin/pegjs

@@ -15,13 +15,6 @@ function printVersion() {
 function printHelp() {
   console.log("Usage: pegjs [options] [--] [<input_file>] [<output_file>]");
   console.log("");
-  console.log("Generates a parser from the PEG grammar specified in the <input_file> and writes");
-  console.log("it to the <output_file>.");
-  console.log("");
-  console.log("If the <output_file> is omitted, its name is generated by changing the");
-  console.log("<input_file> extension to \".js\". If both <input_file> and <output_file> are");
-  console.log("omitted, standard input and output are used.");
-  console.log("");
   console.log("Options:");
   console.log("  -e, --export-var <variable>        name of a global variable into which the");
   console.log("                                     parser object is assigned to when no module");