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_mapped_file_fragment.h b/linker/linker_mapped_file_fragment.h
index 0bfc7a3..f7872bd 100644
--- a/linker/linker_mapped_file_fragment.h
+++ b/linker/linker_mapped_file_fragment.h
@@ -25,8 +25,8 @@
  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
-#ifndef LINKER_MAPPED_FILE_FRAGMENT_H
-#define LINKER_MAPPED_FILE_FRAGMENT_H
+
+#pragma once
 
 #include <unistd.h>
 
@@ -49,5 +49,3 @@
 
   DISALLOW_COPY_AND_ASSIGN(MappedFileFragment);
 };
-
-#endif /* LINKER_MAPPED_FILE_FRAGMENT_H */