[Perf] Update references to telemetry.core.discover

tools/perf/benchmarks/benchmark_smoke_unittest.py

Index: tools/perf/benchmarks/benchmark_smoke_unittest.py
diff --git a/tools/perf/benchmarks/benchmark_smoke_unittest.py b/tools/perf/benchmarks/benchmark_smoke_unittest.py
index 7effd6daa4ca3a415d6e64a10b4379f224b423b1..71cd488947557e60fbf94e3d95e8b59145ddb6d1 100644
--- a/tools/perf/benchmarks/benchmark_smoke_unittest.py
+++ b/tools/perf/benchmarks/benchmark_smoke_unittest.py
@@ -14,12 +14,13 @@ 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