patch 9.0.1389: Amiga: a couple of include files are included twice

Problem:    Amiga: a couple of include files are included twice.
Solution:   Remove duplicate includes. (Ola Söder, closes #12106)
diff --git a/src/os_amiga.c b/src/os_amiga.c
index 2d243b7..bc4ecc9 100644
--- a/src/os_amiga.c
+++ b/src/os_amiga.c
@@ -27,19 +27,19 @@
 #ifndef PROTO
 
 #ifndef LATTICE
-# include <exec/types.h>
 # include <exec/exec.h>
-# include <libraries/dos.h>
 # include <intuition/intuition.h>
 #endif
 
 // XXX These are included from os_amiga.h
+// #include <exec/types.h>
+// #include <libraries/dos.h>
+// #include <libraries/dosextens.h>
 // #include <proto/exec.h>
 // #include <proto/dos.h>
 // #include <proto/intuition.h>
 
 #include <exec/memory.h>
-#include <libraries/dosextens.h>
 
 #include <dos/dostags.h>	    // for 2.0 functions
 #include <dos/dosasl.h>