Test duplicate finder type is not really used by the import media unit test, the only place it is referred to.  We can remove it instead.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9b18b114d768b64cfd7d71225678869083485bee

commit 9b18b114d768b64cfd7d71225678869083485bee
Author: Noel Gordon <noel@chromium.org>
Date: Mon Nov 26 03:39:47 2018

Remove test_duplicate_finder.js

It is instantiated in media_import_handler_unittest, but never used.

Bug:  908290 
Change-Id: Ic3e522ec2a4e14b4fc81a6443d77aa1a7622e70f
Reviewed-on: https://chromium-review.googlesource.com/c/1350013
Commit-Queue: Noel Gordon <noel@chromium.org>
Reviewed-by: Sam McNally <sammc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610760}
[modify] https://crrev.com/9b18b114d768b64cfd7d71225678869083485bee/ui/file_manager/file_manager/background/js/media_import_handler_unittest.html
[modify] https://crrev.com/9b18b114d768b64cfd7d71225678869083485bee/ui/file_manager/file_manager/background/js/media_import_handler_unittest.js
[delete] https://crrev.com/51f7a3cb4379f9902573fc902772657e4cd641a2/ui/file_manager/file_manager/background/js/test_duplicate_finder.js