Make ActivityPrompt a normal class - remove ABC
Parity with JS:
See also:
@@ -20,7 +20,7 @@ from .prompt_recognizer_result import PromptRecognizerResult
from .prompt_validator_context import PromptValidatorContext
-class ActivityPrompt(Dialog, ABC):
+class ActivityPrompt(Dialog):
"""
Waits for an activity to be received.
