Apply misc-include-cleaner fixes

misc-include-cleaner seems to have found a lot more things all of a
sudden.  Unclear why the result has changed, but we can just fix the
issues.

Tested: Clang-tidy now passes.  Code compiles.

Change-Id: Iab045cc183f0daef663b4d5ac901200a42807987
Signed-off-by: Ed Tanous <etanous@nvidia.com>
diff --git a/src/external/ExternalSensor.hpp b/src/external/ExternalSensor.hpp
index c3a7103..495c596 100644
--- a/src/external/ExternalSensor.hpp
+++ b/src/external/ExternalSensor.hpp
@@ -1,11 +1,15 @@
 #pragma once
 
 #include "Thresholds.hpp"
+#include "Utils.hpp"
 #include "sensor.hpp"
 
+#include <sdbusplus/asio/connection.hpp>
 #include <sdbusplus/asio/object_server.hpp>
 
 #include <chrono>
+#include <functional>
+#include <memory>
 #include <string>
 #include <vector>