Headers and block sync should eventually converge to the same result, regardless of whether the peers treat each other as "inbound" or "outbound".
connect_nodes_bi has been introduced as a (temporary?) workaround for bug #5113 and #5138, which has long been fixed in #5157 and #5662.
Thus remove the connect_nodes_bi workaround from the rpc_invalidateblock test.
Conveniently, this also closes #16453. See #16444 (comment) for rationale