You can safely delete the WSDL cache files. If you wish to prevent future caching, use:
ini_set("soap.wsdl_cache_enabled", 0);
or dynamically:
$client = new SoapClient('http://somewhere.com/?wsdl', array('cache_wsdl' => WSDL_CACHE_NONE) );
Remove all wsdl* files in your /tmp folder on the server.
wsdl*
/tmp
WSDL files are cached in your default location for all cache files defined in php.ini. Same location as your session files.
if you already deployed the code or can't change any configuration, you could remove all temp files from wsdl:
rm /tmp/wsdl-*