This reverts commit 74ef838a.

Reason for revert: b/191388102

Original change's description:
> [dirmd] Roll dirmd
>
> This CL picks up
> 1. DIR_METADATA discovery optimization, based on git-ls-files
> 2. Mixin support
> 3. New subcommand "read" that supersedes "export" and "compute"
>
> Last time it was reverted because depot_tools->src got blocked, because
> dirmd was used in Swarming task. The latter was resolved in
> https://chromium-review.googlesource.com/c/chromium/src/+/2921324
>
> Bug: 1201822, 1179786
> Change-Id: I76a580c5d60b506c1f015890fc07817de553975d
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2965866
> Commit-Queue: Nodir Turakulov <nodir@chromium.org>
> Reviewed-by: Dirk Pranke <dpranke@google.com>

Bug: 1201822, 1179786
Change-Id: I6d73267278802a424a6513357f0adda191317535
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2983385
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Nodir Turakulov <nodir@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@google.com>