sensors:sensor: drop unused chrono header

The chrono header is no longer used in this file.

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: Ieca31dfa9166be0cfd5bd84a9aaeef11d30f1b93
diff --git a/sensors/sensor.hpp b/sensors/sensor.hpp
index a447ae0..01f4c02 100644
--- a/sensors/sensor.hpp
+++ b/sensors/sensor.hpp
@@ -2,7 +2,6 @@
 
 #include "interfaces.hpp"
 
-#include <chrono>
 #include <string>
 
 /**