Revert "[File Download Access Prevention] Obfuscate download file for enterprise deep scan"

This reverts commit 6220494c0a64e3b587028bf652a7d376ef7ddab3.

Reason for revert: https://crbug.com/368322459

Original change's description:
> [File Download Access Prevention] Obfuscate download file for enterprise deep scan
>
> Initial implementation of data chunk obfuscation for each download file before they are written to the file.
>
> - Added obfuscator_ to track encryption state for each download.
> - Hash: we also calculate and send the hash of the original file instead when download is complete. We keep doing the hash for the encrypted file. For interrupted downloads we will have an implementation in a subsequent CL.
> - Pass total_bytes to download_file through save_info to protect against truncation. If total_bytes is not given, we append an empty obfuscated chunk at the end instead (20 bytes).
> - Any interrupted errors due to obfuscation operations is returned as DOWNLOAD_INTERRUPT_REASON_FILE_FAILED for now. Will add more detailed errors in a subsequent CL.
> - Support for parallel download is not a priority right now, as it would require changes to the encryption scheme.
>
> Bug: b/349858060
> Change-Id: I10b33afbae2e597b29e2c7e4fe24a7c6b831d116
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5854143
> Reviewed-by: Min Qin <qinmin@chromium.org>
> Reviewed-by: Dominique Fauteux-Chapleau <domfc@chromium.org>
> Commit-Queue: Haihan Chen <haihan@google.com>
> Cr-Commit-Position: refs/heads/main@{#1357084}

Bug: b/349858060
Change-Id: Ibc81cec6b59c3436f2a943b1d896ebdc6d624ee0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5875970
Owners-Override: Peter Pakkenberg <pbirk@chromium.org>
Commit-Queue: Peter Pakkenberg <pbirk@chromium.org>
Reviewed-by: Dominique Fauteux-Chapleau <domfc@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1357690}