Remove Dart_GetScriptSource as it is not used anywhere.

runtime/include/dart_debugger_api.h

Index: runtime/include/dart_debugger_api.h
===================================================================
--- runtime/include/dart_debugger_api.h	(revision 19995)
+++ runtime/include/dart_debugger_api.h	(working copy)
@@ -128,8 +128,6 @@
 
 
 /**
- * DEPRECATED --- use Dart_ScriptGetSource
- *
  * Returns a string containing the source code of the given script
  * in the given library.
  *
@@ -138,20 +136,6 @@
  * \return A handle to string containing the source text if no error
  * occurs.
  */
-DART_EXPORT Dart_Handle Dart_GetScriptSource(
-                            Dart_Handle library_url_in,
-                            Dart_Handle script_url_in);
-
-
-/**
- * Returns a string containing the source code of the given script
- * in the given library.
- *
- * Requires there to be a current isolate.
- *
- * \return A handle to string containing the source text if no error
- * occurs.
- */
 DART_EXPORT Dart_Handle Dart_ScriptGetSource(
                             intptr_t library_id,
                             Dart_Handle script_url_in);