inputflinger: 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: Id257f056972b753f505afe1d253d306bb1824098
diff --git a/services/inputflinger/host/InputDriver.h b/services/inputflinger/host/InputDriver.h
index e56673b..b4c9094 100644
--- a/services/inputflinger/host/InputDriver.h
+++ b/services/inputflinger/host/InputDriver.h
@@ -14,8 +14,7 @@
  * limitations under the License.
  */
 
-#ifndef ANDROID_INPUT_DRIVER_H
-#define ANDROID_INPUT_DRIVER_H
+#pragma once
 
 #include <stdint.h>
 #include <sys/types.h>
@@ -192,4 +191,3 @@
 }
 
 } // namespace android
-#endif // ANDROID_INPUT_DRIVER_H