Remove easy uses of //aos/mutex

I was hoping to get rid of it completely as one of the nontrivial users
of AOS_LOG, but need to write a compatible condition variable first.

Change-Id: I86c1c4084882bf789baabd0255e115d821154830
diff --git a/y2019/BUILD b/y2019/BUILD
index 1d8b996..ddc0a19 100644
--- a/y2019/BUILD
+++ b/y2019/BUILD
@@ -31,8 +31,8 @@
     visibility = ["//visibility:public"],
     deps = [
         "//aos/logging",
-        "//aos/mutex",
         "//aos/network:team_number",
+        "//aos/stl_mutex",
         "//frc971:constants",
         "//frc971/control_loops:pose",
         "//frc971/control_loops:static_zeroing_single_dof_profiled_subsystem",