Problem: Non deterministic teardown

There was a teardown() inside a __del__
which was triggered by the garbage collection
This resulted in an unclear lifecycle and strange log error since the teardown was already triggered before
and made for strange error when running tests

Solution: remove it

src/aleph/vm/hypervisors/firecracker/microvm.py

@@ -503,13 +503,3 @@ async def teardown(self):
             self.config_file_path.unlink(missing_ok=True)
         if Path(self.namespace_path).exists():
             system(f"rm -fr {self.namespace_path}")
-
-    def __del__(self):
-        try:
-            loop = asyncio.get_running_loop()
-            loop.create_task(self.teardown())
-        except RuntimeError as error:
-            if error.args == ("no running event loop",):
-                return
-            else:
-                raise