testplan: Update for new DutAttributes.

- New DutAttributes checked into chromiumos/config don't contain
software attributes (e.g. build target). Refactor testplan to
use only current attributes.

- Plans join BuildMetadata and FlatConfigs to map from software
attributes (e.g. kernel version) to program (in FlatConfigs,
valid dut attribute).

- Delete firmware requirement implementation for now. Maybe be
re-added in future, based on provisioning config in TestPlan
(https://chromium-review.googlesource.com/c/chromiumos/config/+/3176391).

BUG=b:196070598
TEST=CQ

Change-Id: I2cecaa136421933a02318186dbfa923e67c6b596
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/3179313
Reviewed-by: Jaques Clapauch <jaquesc@google.com>
Commit-Queue: Andrew Lamb <andrewlamb@chromium.org>
Tested-by: Andrew Lamb <andrewlamb@chromium.org>
4 files changed