Stop using std::function in HybridEkf

Removes malloc's from the HybridEkf and localizer as a whole.

This solution feels a bit inelegant, but that's true of the entire
HybridEkf class (I may simplify some of this once we delete y2019).

Change-Id: I2deb5b1221ea17b08baad7e8bb46d6bbd1b987a6
Signed-off-by: James Kuszmaul <jabukuszmaul+collab@gmail.com>
diff --git a/y2020/control_loops/drivetrain/localizer_test.cc b/y2020/control_loops/drivetrain/localizer_test.cc
index 9e9e7dd..d280523 100644
--- a/y2020/control_loops/drivetrain/localizer_test.cc
+++ b/y2020/control_loops/drivetrain/localizer_test.cc
@@ -15,6 +15,7 @@
 
 DEFINE_string(output_file, "",
               "If set, logs all channels to the provided logfile.");
+DECLARE_bool(die_on_malloc);
 
 // This file tests that the full 2020 localizer behaves sanely.
 
@@ -146,6 +147,7 @@
     CHECK_EQ(aos::configuration::GetNodeIndex(configuration(), pi1_), 1);
     set_team_id(frc971::control_loops::testing::kTeamNumber);
     set_battery_voltage(12.0);
+    FLAGS_die_on_malloc = true;
 
     if (!FLAGS_output_file.empty()) {
       logger_event_loop_ = MakeEventLoop("logger", roborio_);