Any way to avoid "deprecated function" messages in the Drupal dblog?
The types of PHP errors and warnings being logged to Drupal Watchdog typically reflect the level of error reporting set for the webserver.  If you can edit your vhost config or .htaccess, you could change the error reporting level. Refer to http://php.net/manual/en/errorfunc.constants.php for the different error levels.  

Based on your request, you probably want to disable/exclude error reporting for the following level:


8192     E_DEPRECATED


In .htaccess, you'd add php_admin_value error_reporting 22527 to disable just E_DEPRECATED.  



Should you find that you're still getting other deprecated warnings after applying the change (and possibly restarting server if change was made in vhost), you may want to also exclude the following error level/type:


16384 E_USER_DEPRECATED


See https://stackoverflow.com/questions/5628148/disable-e-deprecated-in-php-error-log for more background on how you can get the bitwise value (error level) for a custom combination of error types.