Add deprecated warning to get_stake_activation method #919

Job	Run time
lint	35s
tests (tests/integration/test_async_http_client.py)	1m 6s
tests (tests/integration/test_async_token_client.py)	1m 15s
tests (tests/integration/test_http_client.py)	1m 11s
tests (tests/integration/test_token_client.py)	1m 12s
tests (tests/integration/test_websockets.py)	2m 20s
tests (tests/integration/test_recent_performance_samples.py)	1m 57s
tests (tests/integration/test_memo.py)	1m 17s
tests (tests/unit)	27s
tests (src)	33s
test	3s
coverage	42s
	12m 38s

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