[infra] Decommission unused `linux-blink-wpt-3pcd-fyi-rel` builder

This CL saves some machine resources by reverting
https://crrev.com/c/6265489:
* The builder has failed continuously since at least mid-August [0], so
  it's unlikely anyone is greening the builder.
* <15 try builds have been created in total, with most appearing to opt
  in because of `wpt` in the name, not because the CLs are 3pcd-related.
* Full rollout of 3pcd has been halted. The existing virtual suite [1]
  targets 3pcd-related codepaths better than broad flag-specific
  coverage. See [2] for when to use virtual vs flag-specific.

[0]: https://ci.chromium.org/ui/p/chromium/builders/ci/linux-blink-wpt-3pcd-fyi-rel?limit=1000
[1]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/web_tests/VirtualTestSuites;l=4401-4424;drc=304aa32636e1fb334cf69a37f72d5755213f1ebc;bpv=0;bpt=0
[2]: https://chromium.googlesource.com/chromium/src/+/HEAD/docs/testing/web_tests.md#Choosing-between-flag_specific-and-virtual-test-suite

Fixed: 391464934
Change-Id: I1c303414f5ed8e26c7761f5d8771d68eb07eb0da
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6923011
Reviewed-by: Xinan Lin <linxinan@chromium.org>
Commit-Queue: Garrett Beaty <gbeaty@google.com>
Reviewed-by: Garrett Beaty <gbeaty@google.com>
Auto-Submit: Jonathan Lee <jonathanjlee@google.com>
Cr-Commit-Position: refs/heads/main@{#1512651}