Remove Lacros skylab builders

lacros-amd64-generic-rel-gtest and lacros-amd64-generic-rel-tast
builders.

Bug: 347103477
Change-Id: I685bf1c74c361b3fdedb3ce7eb3c5909ea93f151
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5798926


Commit-Queue: Sven Zheng <svenzheng@chromium.org>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1343853}