The setting described here has been deprecated in TYPO3 7 and is only used for old code. TYPO3 core itself does not use it anymore, and there is no official way to disable the message.
You could try the skip_page_is_being_generated extension if you don't fear an extension hooking into the core cache :)
If you get this message on your TYPO3 instance, the lockingMode configuration settings is set to disable.
You can configure it in the TYPO3 install tool in the backend, and it is saved in typo3conf/LocalConfiguration.php in TYPO3 6.2:
$TYPO3_CONF_VARS['SYS']['lockingMode'] = 'disable';
The install tool writes about lockingMode:
[SYS][lockingMode] = disable
String: Define which locking mode is used to control requests to pages being generated. Can be one of either disable (no locking), simple (checks for file existance), flock (using PHPs flock() function), semaphore (using PHPs sem_acquire() function).
Default is simple.
The default value on our installation was disable :/