Move AppSearch setSchemaStats and migrationStats to extensions folder.

Those two stats never have any metrics created with them and uploaded to WW before.

Test: Presubmit
Change-Id: Id46daa652bdff0922714616a38590f51619661f5
3 files changed
tree: 1dac967b266a7b6a7c5c583046743929d360c6bd
  1. stats/
  2. OWNERS