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/libc/malloc_debug/debug_log.h b/libc/malloc_debug/debug_log.h
index ed4b541..54dd221 100644
--- a/libc/malloc_debug/debug_log.h
+++ b/libc/malloc_debug/debug_log.h
@@ -26,8 +26,7 @@
  * SUCH DAMAGE.
  */
 
-#ifndef MALLOC_DEBUG_LOG_H
-#define MALLOC_DEBUG_LOG_H
+#pragma once
 
 #include <async_safe/log.h>
 
@@ -42,5 +41,3 @@
     async_safe_write_log(ANDROID_LOG_ERROR, "malloc_debug", (str))
 #define info_log(format, ...)  \
     async_safe_format_log(ANDROID_LOG_INFO, "malloc_debug", (format), ##__VA_ARGS__ )
-
-#endif  // MALLOC_DEBUG_LOG_H