Gtk.TextBuffer.prototype.delete_selection

function delete_selection(interactive:Boolean, default_editable:Boolean):Boolean {
    // Gjs wrapper for gtk_text_buffer_delete_selection()
}

Deletes the range between the "insert" and "selection_bound" marks, that is, the currently-selected text. If interactive is true, the editability of the selection will be considered (users can't delete uneditable text).

interactive: whether the deletion is caused by user interaction
default_editable: whether the buffer is editable by default
Returns: whether there was a non-empty selection to delete