Remove sal.h from fx_system.h.

We do not appear to use any of Microsoft's SAL annotations anywhere
in our code.

Change-Id: I6b9516fbdd51db66a01fa3ac70365aaf70e847b7
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/82832
Commit-Queue: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
diff --git a/core/fxcrt/fx_system.h b/core/fxcrt/fx_system.h
index 9582028..44c739f 100644
--- a/core/fxcrt/fx_system.h
+++ b/core/fxcrt/fx_system.h
@@ -26,7 +26,6 @@
 
 #if defined(OS_WIN)
 #include <windows.h>
-#include <sal.h>
 #endif  // defined(OS_WIN)
 
 #ifdef __cplusplus