This small PR takes use of the message receiving helper functions `wait_for_block()` and `wait_for_header()` in the test `p2p_fingerprint.py`. It also simplifies the checks for very old stale blocks/headers requests by getting rid of the functions `last_block_equals()` and `last_header_equals()` and rather only testing that no blocks/headers message is received at all. Unnecessary sending of requests are also removed and calls to `time.sleep(...)` substituted by ping syncs.
This is a backport of core#20047