Another, perhaps the easiest and most flexible way to do this is through CSS. (what if in the end they will be needed in the future ...).
Looks like:
.ui-dialog-titlebar-close{display:none}
If you want to do this only for some dialogs, you can add the dialogClass: parameter when initializing the dialog, and your css will look like (for example, you added myDialogClass as a dialogClass, so that the entire dialog container will be accessible through this class:
.myDialog .ui-dialog-titlebar-close{display:none}
Good luck setting up!
Bastaller
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