Kill camera_frames queue

Use EventLoop instead.

Change-Id: I39352fecbddd677a32de1a0e77ac11947bc76c6f
diff --git a/y2019/control_loops/drivetrain/camera.q b/y2019/control_loops/drivetrain/camera.q
index 6ef6f49..9d5dffc 100644
--- a/y2019/control_loops/drivetrain/camera.q
+++ b/y2019/control_loops/drivetrain/camera.q
@@ -8,6 +8,8 @@
   float skew;
 };
 
+// Frames from a camera.
+// Published on ".y2019.control_loops.drivetrain.camera_frames"
 message CameraFrame {
   // Number of nanoseconds since the aos::monotonic_clock epoch at which this
   // frame was captured.
@@ -22,5 +24,3 @@
   // Index of the camera position (not serial number) which this frame is from.
   uint8_t camera;
 };
-
-queue CameraFrame camera_frames;