gn2bp: remove unused toolchain property

This has been replaced by target.arch.

Test: //components/cronet/android:cronet
Change-Id: If0193d549fbe50ab9b5197e186e41ffff3ca6e09
diff --git a/tools/gn2bp/gn_utils.py b/tools/gn2bp/gn_utils.py
index d1d8319..27fbdb2 100644
--- a/tools/gn2bp/gn_utils.py
+++ b/tools/gn2bp/gn_utils.py
@@ -271,8 +271,6 @@
       return target  # Target already processed.
 
     target.testonly = desc.get('testonly', False)
-    # TODO: remove toolchain from Target object
-    target.toolchain = desc.get('toolchain', None)
 
     proto_target_type, proto_desc = self.get_proto_target_type(gn_desc, gn_target_name)
     if proto_target_type is not None: