libinput: Use #pragma once instead of explicit define guards

The #pragma once directive is commonly used by modern cpp code, and
support for its use in Andorid is proposed in go/droidcppstyle.

Bug: 245989146
Test: Build, Presubmit
Change-Id: Ib7852f1a343864dff46e7bc616d707bc7d5bf512
diff --git a/include/input/PropertyMap.h b/include/input/PropertyMap.h
index b1e3f85..28e4816 100644
--- a/include/input/PropertyMap.h
+++ b/include/input/PropertyMap.h
@@ -14,8 +14,7 @@
  * limitations under the License.
  */
 
-#ifndef _UTILS_PROPERTY_MAP_H
-#define _UTILS_PROPERTY_MAP_H
+#pragma once
 
 #include <android-base/result.h>
 #include <utils/Tokenizer.h>
@@ -98,5 +97,3 @@
 };
 
 } // namespace android
-
-#endif // _UTILS_PROPERTY_MAP_H