[Perf] Update references to telemetry.core.discover

tools/perf/core/find_dependencies.py

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import fnmatch
 import imp
 import logging
 import optparse
 import os
 import sys
 import zipfile
 
 from telemetry import benchmark
-from telemetry.core import discover
 from telemetry.internal.util import command_line
 from telemetry.internal.util import path
 from telemetry.internal.util import path_set
 
+from py_utils import discover
+
 try:
   from modulegraph import modulegraph  # pylint: disable=import-error
 except ImportError as err:
   modulegraph = None
   import_error = err
 
 from core import bootstrap
 from core import path_util
 
 DEPS_FILE = 'bootstrap_deps'
@@ skipping 214 matching lines @@
 
   def Run(self, args):
     target_paths = args.positional_args
     dependencies = FindDependencies(target_paths, args)
     if args.zip:
       ZipDependencies(target_paths, dependencies, args)
       print 'Zip archive written to %s.' % args.zip
     else:
       print '\n'.join(sorted(dependencies))
     return 0