Revert "personalization: CurrentWallpaper key not identify custom wallpapers"

This reverts commit 343b6014f77c02cca0da4cb3eaf1035087f042a4.

Reason for revert: causing crash during startup (crbug.com/1342983)

Original change's description:
> personalization: CurrentWallpaper key not identify custom wallpapers
>
> For custom wallpapers, the CurrentWallpaper key is set to the image's
> filename which made the UI mistakenly highlight multiple files with
> same name. To fix, add user_file_path field which is the full path of
> the file in WallpaperInfo and use this as CurrentWallpaper key to be
> uniquely identify custom wallpapers.
>
> BUG=b:229420564
> TEST=browser_tests --gtest_filter="*PersonalizationAppComponent*"
> TEST=browser_tests --gtest_filter="*PersonalizationAppController*"
> TEST=ash_unittests --gtest_filter="*WallpaperControllerTest*"
> TEST=ash_unittests --gtest_filter="*WallpaperPrefManagerTest*"
>
> Cq-Include-Trybots: luci.chrome.try:linux-chromeos-chrome
> Change-Id: Ief6e3a27f56347d4e04d8dc680c50920a58adc9f
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3736750
> Commit-Queue: Thuong Phan <thuongphan@chromium.org>
> Reviewed-by: Jeffrey Young <cowmoo@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1022008}

Bug: b:229420564, 1342983
Change-Id: I283a77e3781e352dc401cfb299962fdabd52f0e1
Cq-Include-Trybots: luci.chrome.try:linux-chromeos-chrome
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3752628
Commit-Queue: Mitsuru Oshima <oshima@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1022189}