Revert "Add ObfuscatedFileUtilMemoryDelegate."

This reverts commit 4eac21ba4722b126e8aee24f0be61d348e35b361.

Reason for revert: <INSERT REASONING HERE>
See crbug.com/930762

Original change's description:
> Add ObfuscatedFileUtilMemoryDelegate.
>
> |ObfuscatedFileUtilDelegate| and |ObfuscatedFileUtilMemoryDelegate|
> are added to support in-memory file system for incognito mode and
> |ObfuscatedFileUtil| is updated to choose the appropriate delegate
> based on being incognito or not.
>
> To avoid making the CL large, only the skeleton of the
> |ObfuscatedFileUtilMemoryDelegate| is added in this CL and the actual
> implementation will be added in a next one.
>
> The change is part of the following design doc:
> https://docs.google.com/document/d/17NV1cGSIEG2i5qm2QU4EzDMKRoyVEbNNq-Re-JhwSB0
>
> Bug: 93417
> Change-Id: I47353c656ab70ab6c98c8e06c9e0c3a03319d012
> Reviewed-on: https://chromium-review.googlesource.com/c/1452176
> Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
> Commit-Queue: Ramin Halavati <rhalavati@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#630002}

TBR=mek@chromium.org,rhalavati@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 93417,930762
Change-Id: Ibe4fc302b5691d0cda090521384eb8c7ff6e3dbf
Reviewed-on: https://chromium-review.googlesource.com/c/1464206
Reviewed-by: David Tseng <dtseng@chromium.org>
Commit-Queue: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#630874}
9 files changed