[Perf] Update references to telemetry.core.discover

tools/perf/benchmarks/benchmark_smoke_unittest.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.
 
 """Run the first page of one benchmark for every module.
 
 Only benchmarks that have a composable measurement are included.
 Ideally this test would be comprehensive, however, running one page
 of every benchmark would run impractically long.
 """
 
 import os
 import sys
 import unittest
 
 from telemetry import benchmark as benchmark_module
-from telemetry.core import discover
 from telemetry import decorators
 from telemetry.internal.browser import browser_finder
 from telemetry.testing import options_for_unittests
 from telemetry.testing import progress_reporter
 
+from py_utils import discover
+
 from benchmarks import battor
 from benchmarks import image_decoding
 from benchmarks import indexeddb_perf
 from benchmarks import jetstream
 from benchmarks import kraken
 from benchmarks import octane
 from benchmarks import rasterize_and_record_micro
 from benchmarks import speedometer
 from benchmarks import v8_browsing
 
@@ skipping 115 matching lines @@
     MergeDecorators(method, disabled_method_attr, benchmark,
                     disabled_benchmark_attr)
     MergeDecorators(method, enabled_method_attr, benchmark,
                     enabled_benchmark_attr)
 
     setattr(BenchmarkSmokeTest, benchmark.Name(), method)
 
     suite.addTest(BenchmarkSmokeTest(benchmark.Name()))
 
   return suite