[bazel] Don't run Bazel actions in any pool

The queued Bazel actions take up pool slots (which is an issue in ninja
that should be separately fixed). Switch Bazel actions to use the
default pool to minimum their impact on the build until that issue is
fixed.

Bug: 556911936
Change-Id: I00c90660884c697a09c40f0d5651d11f6a6a6964
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1805399
Fuchsia-Auto-Submit: Aaron Wood <aaronwood@google.com>
Commit-Queue: Aaron Wood <aaronwood@google.com>
Reviewed-by: David Fang <fangism@google.com>