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/y2020/BUILD b/y2020/BUILD
index 38832b8..208b04a 100644
--- a/y2020/BUILD
+++ b/y2020/BUILD
@@ -55,8 +55,8 @@
     visibility = ["//visibility:public"],
     deps = [
         "//aos/logging",
-        "//aos/mutex",
         "//aos/network:team_number",
+        "//aos/stl_mutex",
         "//frc971:constants",
         "//frc971/control_loops:static_zeroing_single_dof_profiled_subsystem",
         "//y2020/control_loops/drivetrain:polydrivetrain_plants",
diff --git a/y2020/constants.cc b/y2020/constants.cc
index 131b0de..d39e1cd 100644
--- a/y2020/constants.cc
+++ b/y2020/constants.cc
@@ -10,8 +10,8 @@
 
 #include "absl/base/call_once.h"
 #include "aos/logging/logging.h"
-#include "aos/mutex/mutex.h"
 #include "aos/network/team_number.h"
+#include "aos/stl_mutex/stl_mutex.h"
 #include "y2020/control_loops/superstructure/control_panel/integral_control_panel_plant.h"
 #include "y2020/control_loops/superstructure/hood/integral_hood_plant.h"
 #include "y2020/control_loops/superstructure/intake/integral_intake_plant.h"
@@ -156,8 +156,8 @@
 }
 
 const Values &GetValuesForTeam(uint16_t team_number) {
-  static ::aos::Mutex mutex;
-  ::aos::MutexLocker locker(&mutex);
+  static aos::stl_mutex mutex;
+  std::unique_lock<aos::stl_mutex> locker(mutex);
 
   // IMPORTANT: This declaration has to stay after the mutex is locked to
   // avoid race conditions.