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_allocator.h b/linker/linker_allocator.h
index 7fc6cbf..82e4ef4 100644
--- a/linker/linker_allocator.h
+++ b/linker/linker_allocator.h
@@ -26,8 +26,7 @@
  * SUCH DAMAGE.
  */
 
-#ifndef __LINKER_ALLOCATOR_H
-#define __LINKER_ALLOCATOR_H
+#pragma once
 
 #include <errno.h>
 #include <stdlib.h>
@@ -152,6 +151,3 @@
   LinkerSmallObjectAllocator* allocators_;
   uint8_t allocators_buf_[sizeof(LinkerSmallObjectAllocator)*kSmallObjectAllocatorsCount];
 };
-
-
-#endif  /* __LINKER_ALLOCATOR_H */