distbuild: Remove the build-steps message

This message was hundreds of kilobytes in size, as it contained a
recursive list of dependencies for each artifact in the build graph. It
was used in the initiator only to print this message:

    Build steps in total: 592

This message is now gone. The 'Need to build %d artifacts'
build-progress message now indicates the total build steps instead:

    Need to build 300 artifacts, of 592 total

This is a compatible change to the distbuild protocol: old initiators
will continue to work as normal with new controllers that don't send
the build-steps message.

1 files changed, 2 insertions, 3 deletions

diff --git a/distbuild/__init__.py b/distbuild/__init__.py
index 0bfae6e9..62a904d4 100644
--- a/distbuild/__init__.py
+++ b/distbuild/__init__.py
@@ -51,9 +51,8 @@ from worker_build_scheduler import (WorkerBuildQueuer,
                                     WorkerBuildFailed,
                                     WorkerBuildStepStarted)
 from build_controller import (BuildController, BuildFailed, BuildProgress,
-                              BuildSteps, BuildStepStarted,
-                              BuildStepAlreadyStarted, BuildOutput,
-                              BuildStepFinished, BuildStepFailed,
+                              BuildStepStarted, BuildStepAlreadyStarted,
+                              BuildOutput, BuildStepFinished, BuildStepFailed,
                               BuildFinished, BuildCancel,
                               build_step_name, map_build_graph)
 from initiator import Initiator