[Mahi] Remove the magic boost resources from chrome/browser

The magic boost related code was removed from chrome/browser by cl
https://chromium-review.googlesource.com/c/chromium/src/+/5618993
(The corresponding logic was refactored and moved to ash/).

This cl cleaned up the unused image json file.

Bug: b/341832244
Change-Id: I2a91d9222d72dce1954a87fb504f04b6b2720cb6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5677726


Commit-Queue: Jiaming Cheng <jiamingc@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1324399}