Revert "Change to default directory when removable entry list is unmounted."

This reverts commit 499a46c274415cbae3dc022fd13d4ee6b2c6bddb.

Reason for revert:

Findit (https://goo.gl/kROfz5) identified CL at revision 632481 as the
culprit for failures in the build cycles as shown on:
https://findit-for-me.appspot.com/waterfall/culprit?key=ag9zfmZpbmRpdC1mb3ItbWVyRAsSDVdmU3VzcGVjdGVkQ0wiMWNocm9taXVtLzQ5OWE0NmMyNzQ0MTVjYmFlM2RjMDIyZmQxM2Q0ZWU2YjJjNmJkZGIM

Sample Failed Build: https://ci.chromium.org/buildbot/chromium.memory/Linux%20Chromium%20OS%20ASan%20LSan%20Tests%20%281%29/31559

Sample Failed Step: webui_polymer2_browser_tests

Original change's description:
> Change to default directory when removable entry list is unmounted.
> 
> Fixes bug where file list and breadcrumbs don't updated after removable
> entry lists are unmounted.
> Added unmount for removable test volumes, to test an unmount event.
> 
> Bug: 918795
> Change-Id: I13ea71b6db9dff5ac2e59982eef7f6e34457fe31
> Reviewed-on: https://chromium-review.googlesource.com/c/1465962
> Commit-Queue: Alli Murray <alliemurray@google.com>
> Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#632481}

Change-Id: I42f3409091357110d967dfb6e20e7676e849f5a5
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 918795
Reviewed-on: https://chromium-review.googlesource.com/c/1474699
Cr-Commit-Position: refs/heads/master@{#632527}
9 files changed