Revert team and thread changes for COMPAT_MODE (hrev52010 & hrev52011).

This reverts commit c558f9c8fe.
This reverts commit 44f24718b1.
This reverts commit a69cb33030.
This reverts commit 951182620e.

There have been multiple reports that these changes break mounting NTFS partitions
(on all systems, see #14204), and shutting down (on certain systems, see #12405.)
Until they can be fixed, they are being backed out.

headers/private/system/thread_defs.h

@@ -37,10 +37,6 @@ enum {
 #define THREAD_CREATION_FLAG_DEFER_SIGNALS	0x01
 	// create the thread with signals deferred, i.e. with
 	// user_thread::defer_signals set to 1
-#ifdef _COMPAT_MODE
-#	define THREAD_CREATION_FLAG_COMPAT_MODE	0x02
-	// create the thread with a compatibility mode
-#endif
 
 
 struct thread_creation_attributes {