TUTORIAL.md Adjust firmware dependency notes after V1.15 realease.

Author: peterhinch

v3/docs/TUTORIAL.md

@@ -892,6 +892,8 @@ asyncio.run(queue_go(4))
 
 ## 3.6 ThreadSafeFlag
 
+This requires firmware V1.15 or later.
+
 This official class provides an efficient means of synchronising a task with a
 truly asynchronous event such as a hardware interrupt service routine or code
 running in another thread. It operates in a similar way to `Event` with the
@@ -974,11 +976,6 @@ tasks may wait on that `Event`. As an alternative to explicitly coding this,
 the [Message class](./TUTORIAL.md#39-message) uses this approach to provide an
 `Event`-like object which can be triggered from an ISR.
 
-#### Note
-
-ThreadSafeFlag is only available in nightly builds. It will be available in
-release builds starting with V1.15.
-
 ###### [Contents](./TUTORIAL.md#contents)
 
 ## 3.7 Barrier
@@ -1188,6 +1185,8 @@ finally:
 
 ## 3.9 Message
 
+This requires firmware V1.15 or later.
+
 This is an unofficial primitive with no counterpart in CPython asyncio. It uses
 [ThreadSafeFlag](./TUTORIAL.md#36-threadsafeflag) to provide an object similar
 to `Event` but capable of being set in a hard ISR context. It extends
@@ -1275,11 +1274,6 @@ async def main():
 asyncio.run(main())
 ```
 
-#### ThreadSafeFlag dependency
-
-ThreadSafeFlag is only available in nightly builds. It will be available in
-release builds starting with V1.15.
-
 ## 3.10 Synchronising to hardware
 
 The following hardware-related classes are documented [here](./DRIVERS.md):