CLEANUP: checks: don't report report the fork() error twice

CLEANUP: checks: don't report report the fork() error twice

Upon fork() error, a first report is immediately made by connect_proc_chk()
via set_server_check_status(), then process_chk_proc() detects the error
code and makes up a dummy connection error to call chk_report_conn_err(),
which tries to retrieve the errno code from the connection, fails, then
saves the status message from the check, fails all "if" tests on its path
related to the connection then resets the check's state to the current one
with the current status message. All this useless chain is the only reason
why process checks require a connection! Let's simply get rid of this second
useless call.