MINOR: checks: Remove dead code from process_chk_conn()

MINOR: checks: Remove dead code from process_chk_conn()

With the checks refactoring, all connections are performed into a tcp-check
ruleset. So, in process_chk_conn(), it is no longer required to check
synchronous error on the connect when an health check is started. This part is
now handled in tcpcheck_main(). And because it is impossible to start a health
check with a connection, all tests on the connection during the health check
startup can be safely removed.

This patch should fix the issue #636. No backport needed.