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/reader/mapper/MultiTouchInputMapper.h b/services/inputflinger/reader/mapper/MultiTouchInputMapper.h
index fe8af5d..212c9c9 100644
--- a/services/inputflinger/reader/mapper/MultiTouchInputMapper.h
+++ b/services/inputflinger/reader/mapper/MultiTouchInputMapper.h
@@ -14,8 +14,7 @@
  * limitations under the License.
  */
 
-#ifndef _UI_INPUTREADER_MULTI_TOUCH_INPUT_MAPPER_H
-#define _UI_INPUTREADER_MULTI_TOUCH_INPUT_MAPPER_H
+#pragma once
 
 #include "TouchInputMapper.h"
 
@@ -122,5 +121,3 @@
 };
 
 } // namespace android
-
-#endif // _UI_INPUTREADER_MULTI_TOUCH_INPUT_MAPPER_H
\ No newline at end of file