Fix incorrect path in python2 GN templates.

A couple of the python2 action GN templates referenced
the wrong (old) path to //build/util/python2_action.py.
This CL fixes them.

Bug: 1112471
Change-Id: Ifb1c35ef00275e79f6f63fe9b3afac28b24aa975
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2510990Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Dirk Pranke <dpranke@google.com>
Cr-Commit-Position: refs/heads/master@{#822862}

build/config/python.gni

@@ -133,7 +133,7 @@ template("python2_action_foreach") {
                              "visibility",
                            ])
 
-    script = "//build/run_under_python2.py"
+    script = "//build/util/python2_action.py"
     if (!defined(invoker.inputs)) {
       inputs = [ invoker.script ]
     } else {
@@ -202,7 +202,7 @@ template("action_with_pydeps") {
       _args = args
       args = []
       args = [ rebase_path(invoker.script, root_build_dir) ] + _args
-      script = "//build/run_under_python2.py"
+      script = "//build/util/python2_action.py"
     }
   }
 }
@@ -251,7 +251,7 @@ template("action_foreach_with_pydeps") {
       _args = args
       args = []
       args = [ rebase_path(invoker.script, root_build_dir) ] + _args
-      script = "//build/run_under_python2.py"
+      script = "//build/util/python2_action.py"
     }
   }
 }