Update standalone help message for removed legacy debugger protocol options.

runtime/bin/main.cc

Index: runtime/bin/main.cc
diff --git a/runtime/bin/main.cc b/runtime/bin/main.cc
index 29485e200f17fc90e125686a6fc50b6b3d95d291..f8ef12f0fc5fb1b1bcb469e9aa8ce66bc4119806 100644
--- a/runtime/bin/main.cc
+++ b/runtime/bin/main.cc
@@ -882,15 +882,6 @@ static void PrintUsage() {
 "--version\n"
 "  Print the VM version.\n"
 "\n"
-"--debug[:<port number>]\n"
-"  enables debugging and listens on specified port for debugger connections\n"
-"  (default port number is 5858)\n"
-"\n"
-"--break-at=<location>\n"
-"  sets a breakpoint at specified location where <location> is one of :\n"
-"  url:<line_num> e.g. test.dart:10\n"
-"  [<class_name>.]<function_name> e.g. B.foo\n"
-"\n"
 "--snapshot=<file_name>\n"
 "  loads Dart script and generates a snapshot in the specified file\n"
 "\n"