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They don't need to run in Chrome's unit_tests suite any more.

* Move ExtensionL10UtilTest
* Move FileUtilTest
* Keep browser action and page action tests in Chrome, since those are
  Chrome-specific concepts

This CL depends on https://codereview.chromium.org/565423003/ for cleanup
of _manifest_features.json

BUG=397165
TEST=extensions_unittests, unit_tests

Review URL: https://codereview.chromium.org/562273006

Cr-Commit-Position: refs/heads/master@{#295605}