Remove unnecessary libavutil/(avutil|common|internal).h inclusions

Some of these were made possible by moving several common macros to
libavutil/macros.h.

While just at it, also improve the other headers a bit.

Reviewed-by: Martin Storsjö <martin@martin.st>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavutil/mem.c

@@ -37,10 +37,13 @@
 #include <malloc.h>
 #endif
 
-#include "avutil.h"
-#include "common.h"
+#include "attributes.h"
+#include "avassert.h"
 #include "dynarray.h"
+#include "error.h"
+#include "internal.h"
 #include "intreadwrite.h"
+#include "macros.h"
 #include "mem.h"
 
 #ifdef MALLOC_PREFIX
@@ -59,8 +62,6 @@ void  free(void *ptr);
 
 #endif /* MALLOC_PREFIX */
 
-#include "mem_internal.h"
-
 #define ALIGN (HAVE_AVX512 ? 64 : (HAVE_AVX ? 32 : 16))
 
 /* NOTE: if you want to override these functions with your own