Switch the rest of our internal headers to #pragma once.

We've been using #pragma once for new internal files, but let's be more bold.

Bug: N/A
Test: builds
Change-Id: I7e2ee2730043bd884f9571cdbd8b524043030c07
diff --git a/linker/linker_config.h b/linker/linker_config.h
index 0c50d57..e117aea 100644
--- a/linker/linker_config.h
+++ b/linker/linker_config.h
@@ -26,8 +26,7 @@
  * SUCH DAMAGE.
  */
 
-#ifndef _LINKER_CONFIG_H_
-#define _LINKER_CONFIG_H_
+#pragma once
 
 #include <android/api-level.h>
 
@@ -171,5 +170,3 @@
 
   DISALLOW_COPY_AND_ASSIGN(Config);
 };
-
-#endif /* _LINKER_CONFIG_H_ */