- Remove the legacy debug protocol.

BUG=
[email protected]

Review URL: https://codereview.chromium.org/1497033003 .

Author: iposva-google

runtime/bin/builtin_impl_sources.gypi

@@ -16,17 +16,6 @@
     'builtin_common.cc',
     'dartutils.cc',
     'dartutils.h',
-    'dbg_connection.cc',
-    'dbg_connection.h',
-    'dbg_connection_android.cc',
-    'dbg_connection_linux.cc',
-    'dbg_connection_linux.h',
-    'dbg_connection_macos.cc',
-    'dbg_connection_macos.h',
-    'dbg_connection_win.cc',
-    'dbg_connection_win.h',
-    'dbg_message.h',
-    'dbg_message.cc',
     'directory.cc',
     'directory.h',
     'directory_android.cc',