Revert "libbinder: Replace deprecated utils/threads.h header"

This reverts commit bc8d5b4830d7fb5afe52f9d8809212babedd72b1.

Reason for revert: breaks libvrflinger build

Change-Id: I767dbf3ed56893ead497184d2204a04156faaa9d
diff --git a/libs/binder/IMemory.cpp b/libs/binder/IMemory.cpp
index d0cb1f3..bd974b0 100644
--- a/libs/binder/IMemory.cpp
+++ b/libs/binder/IMemory.cpp
@@ -32,7 +32,7 @@
 #include <log/log.h>
 
 #include <utils/KeyedVector.h>
-#include <utils/Mutex.h>
+#include <utils/threads.h>
 
 #define VERBOSE   0