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/BlockingQueue.h b/services/inputflinger/BlockingQueue.h
index 8300e8a..fe37287 100644
--- a/services/inputflinger/BlockingQueue.h
+++ b/services/inputflinger/BlockingQueue.h
@@ -14,8 +14,7 @@
  * limitations under the License.
  */
 
-#ifndef _UI_INPUT_BLOCKING_QUEUE_H
-#define _UI_INPUT_BLOCKING_QUEUE_H
+#pragma once
 
 #include "android-base/thread_annotations.h"
 #include <condition_variable>
@@ -106,6 +105,4 @@
     std::vector<T> mQueue GUARDED_BY(mLock);
 };
 
-
 } // namespace android
-#endif