tests/extmod: Remove asyncio .exp files that match CPython output.

These were added back in commit c4935f3
because the tests required CPython 3.8, which was quite new at the time.
But CPython 3.8 was released over 4 years ago (October 2019) and the CI
test runners, and developers, have this (or a more recent) CPython version.

Removing the .exp files also helps keep MicroPython semantics the same as
CPython.

The asyncio_fair.py test it adjusted slightly to have more deterministic
timing and output.

Signed-off-by: Damien George <[email protected]>

Author: dpgeorge

tests/extmod/asyncio_await_return.py.exp

@@ -20,7 +20,7 @@ async def main():
     t2 = asyncio.create_task(task(2, 0.1))
     t3 = asyncio.create_task(task(3, 0.18))
     t4 = asyncio.create_task(task(4, -100))
-    await asyncio.sleep(0.5)
+    await asyncio.sleep(0.45)  # t2 prints 5 times, t3 prints 3 times
     t1.cancel()
     t2.cancel()
     t3.cancel()

tests/extmod/asyncio_basic2.py.exp

@@ -1,4 +1,8 @@
 # Test Lock class
+#
+# This test has a corresponding .exp file because it tests a very specific ordering of
+# events when cancelling a task waiting on a lock, and that ordering should not change
+# (even though it does match CPython's output).
 
 try:
     import asyncio