Split up zeroing library BUILD rules

There was no good reason for one build rule to have both the interface
and a bunch of implementations; split it up and make the relevant users
depend on the libraries directly.

Change-Id: If6a0aa49dd7ea588b7325604658bc0594db4aac0
Signed-off-by: James Kuszmaul <jabukuszmaul+collab@gmail.com>
diff --git a/y2020/control_loops/superstructure/BUILD b/y2020/control_loops/superstructure/BUILD
index d1f20a2..83af834 100644
--- a/y2020/control_loops/superstructure/BUILD
+++ b/y2020/control_loops/superstructure/BUILD
@@ -83,6 +83,9 @@
         "//frc971/control_loops:control_loop",
         "//frc971/control_loops:control_loops_fbs",
         "//frc971/control_loops/drivetrain:drivetrain_status_fbs",
+        "//frc971/zeroing:absolute_and_absolute_encoder",
+        "//frc971/zeroing:absolute_encoder",
+        "//frc971/zeroing:pot_and_absolute_encoder",
         "//y2020:constants",
         "//y2020/control_loops/superstructure/hood:hood_encoder_zeroing_estimator",
         "//y2020/control_loops/superstructure/shooter",