[Telemetry] Move maps recording to public.

Maps folks have confirmed that it is public data, the same you'd get by
visiting the site.

BUG=

Review URL: https://codereview.chromium.org/526833002

Cr-Commit-Position: refs/heads/master@{#292938}

tools/perf/page_sets/maps.py

@@ -38,6 +38,6 @@ class MapsPageSet(page_set_module.PageSet):
   def __init__(self):
     super(MapsPageSet, self).__init__(
         archive_data_file='data/maps.json',
-        bucket=page_set_module.INTERNAL_BUCKET)
+        bucket=page_set_module.PUBLIC_BUCKET)
 
     self.AddPage(MapsPage(self))