Python client is deprecated.

This removes all references to swarming_client in this repository.
https://source.chromium.org/search?q=swarming_client&sq=&ss=chromium%2Fchromium%2Fsrc:v8%2F

Bug: chromium:984869
Change-Id: I377c47fc696723ae4ba53418682f6e06129812f9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3114156
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Liviu Rau <liviurau@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76452}