[tests] Remove maxblocksinflight testcase

maxblocksinflight tested that a node would not send get_data messages
for more than 16 new blocks at the same time. bitcoin core no longer
responds to block invs with get_data, since it does headers-first
sync'ing. This test was therefore testing nothing and can be removed.

the sendheaders test script tests that bitcoin will not send get_headers
for more than 16 blocks simultaneously.

test/functional/test_runner.py

@@ -135,7 +135,6 @@ EXTENDED_SCRIPTS = [
     'txn_clone.py --mineblock',
     'forknotify.py',
     'invalidateblock.py',
-    'maxblocksinflight.py',
     'p2p-acceptblock.py',
     'replace-by-fee.py',
 ]