doc: Remove no longer correct comment

Left over since fa7b07571f.

Co-authored-by: Lőrinc <pap.lorinc@gmail.com>

test/functional/test_framework/test_node.py

@@ -575,8 +575,6 @@ class TestNode():
     def busy_wait_for_debug_log(self, expected_msgs, timeout=60):
         """
         Block until we see a particular debug log message fragment or until we exceed the timeout.
-        Return:
-            the number of log lines we encountered when matching
         """
         time_end = time.time() + timeout * self.timeout_factor
         prev_size = self.debug_log_size(mode="rb")  # Must use same mode that is used to read() below