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