Remove --local_test_jobs from bazelci.py

[meteorcloudy]

Remove --local_test_jobs and concurrent_test_jobs() from execute_bazel_test and execute_bazel_coverage in bazelci.py.

Why

1. Disables Bazel's CPU/RAM resource scheduler for tests: When --local_test_jobs is set to a non-zero value, Bazel's TestTargetProperties.getLocalResourceUsage() assigns cpu=0 and memory=0 to all test actions (unless explicitly tagged with cpu:N or resources:...), ignoring test size memory estimates (small/medium/large/enormous) and allowing build + test actions to oversubscribe host CPUs during mixed compilation/test phases.
2. Warnings on ARM64 Linux (c4a-standard-8): concurrent_jobs sets --jobs=8 (cpu_count()), while concurrent_test_jobs hardcoded --local_test_jobs=12, causing Bazel to emit a warning on every test/coverage run (WARNING: High value for --local_test_jobs: 12. This exceeds the value for --jobs: 8.).
3. Underutilization on 30-core Linux/Windows VMs (c2-standard-30): Hardcoding --local_test_jobs to 12 on Linux and 8 on Windows left 60%–73% of CPU cores idle during pure test execution phases.
4. Projects that need specific concurrency limits (like Bazel's own CI on macOS) already configure --local_test_jobs in their .bazelci/presubmit.yml.

[meteorcloudy]

Also tested on Bazel via bazelbuild/bazel#31171

[meteorcloudy]

Looks like this actually causing tests to be flaky on windows, I need to investigate more