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_utils.h b/linker/linker_utils.h
index e104a25..214646c 100644
--- a/linker/linker_utils.h
+++ b/linker/linker_utils.h
@@ -26,8 +26,7 @@
  * SUCH DAMAGE.
  */
 
-#ifndef __LINKER_UTILS_H
-#define __LINKER_UTILS_H
+#pragma once
 
 #include <string>
 #include <vector>
@@ -56,5 +55,3 @@
 off64_t page_start(off64_t offset);
 size_t page_offset(off64_t offset);
 bool safe_add(off64_t* out, off64_t a, size_t b);
-
-#endif