Switch BionicDeathTest to `#pragma once`.

Test: treehugger
Change-Id: I3daded12812fb579e8b7d7abeb885ee7f17032e3
diff --git a/tests/BionicDeathTest.h b/tests/BionicDeathTest.h
index 6826ab7..f70839a 100644
--- a/tests/BionicDeathTest.h
+++ b/tests/BionicDeathTest.h
@@ -14,8 +14,7 @@
  * limitations under the License.
  */
 
-#ifndef BIONIC_TESTS_BIONIC_DEATH_TEST_H_
-#define BIONIC_TESTS_BIONIC_DEATH_TEST_H_
+#pragma once
 
 #include <signal.h>
 
@@ -44,5 +43,3 @@
  private:
   struct sigaction64 previous_;
 };
-
-#endif // BIONIC_TESTS_BIONIC_DEATH_TEST_H_