You should be able to do this by changing your ssh configuration from the default log-level of "info" to "error" (the next level up).
Refer to the
ssh_config manual page:
Gives the verbosity level that is used when logging messages from ssh(1). The possible values are:
DEBUG3. The default is
DEBUG1 are equivalent.
DEBUG3 each specify higher levels of verbose output.
The source code for
ssh tells the story:
* Initialize "log" output. Since we are the client all output
* actually goes to stderr.
log_init(av, options.log_level == -1 ? SYSLOG_LEVEL_INFO : options.log_level,
along with the definition of
log_init(char *av0, LogLevel level, SyslogFacility facility, int on_stderr)
i.e., all of the "log" messages go to the standard error, and you can only adjust how many you get. The one you do not want happens to be at the