Move camera.h to the frc971/ folder

The code for dealing with camera transformations is reasonably
year-generic, so move it into frc971/.

Change-Id: I7751ccd01c3e45093c8e548d65e0087b615f0ae0
diff --git a/y2019/BUILD b/y2019/BUILD
index 328c93f..e286fc7 100644
--- a/y2019/BUILD
+++ b/y2019/BUILD
@@ -36,7 +36,7 @@
         "//frc971:constants",
         "//frc971/control_loops:pose",
         "//frc971/control_loops:static_zeroing_single_dof_profiled_subsystem",
-        "//y2019/control_loops/drivetrain:camera",
+        "//frc971/control_loops/drivetrain:camera",
         "//y2019/control_loops/drivetrain:polydrivetrain_plants",
         "//y2019/control_loops/superstructure/elevator:elevator_plants",
         "//y2019/control_loops/superstructure/intake:intake_plants",