Break dependency from droid_targets to blueprint_tools

But only for a TARGET_BUILD_UNBUNDLED_IMAGE build. Since
the unbundled image build attempts to remove as many
framework sources as possible, we'd like to remove the
sources and dependencies of some blueprint_tools as
well.

Test: m nothing dist
Test: Verify graph is unchanged
Test: m nothing dist TARGET_BUILD_UNBUNDLED_IMAGE=true
Test: Verify that graph no longer includes blueprint_tools
Bug: 192629969
Change-Id: Ibfb52b841379e20855d0a935a13ad047af2fe58d