contentControlDelete.js

// Run a batch operation against the Word object model.
Word.run(function (context) {
    
    // Create a proxy object for the content controls collection.
    var contentControls = context.document.contentControls;
    
    // Queue a command to load the content controls collection.
    contentControls.load('text');
     
    // Synchronize the document state by executing the queued-up commands, 
    // and return a promise to indicate task completion.
    return context.sync().then(function () {
        
        if (contentControls.items.length === 0) {
            console.log("There isn't a content control in this document.");
        } else {
            
            // Queue a command to delete the first content control. The
            // contents will remain in the document.
            contentControls.items[0].delete(true);
            // Synchronize the document state by executing the queued-up commands, 
            // and return a promise to indicate task completion.
            return context.sync().then(function () {
                console.log('Content control cleared of contents.');
            });      
        }
            
    });  
})
.catch(function (error) {
    console.log('Error: ' + JSON.stringify(error));
    if (error instanceof OfficeExtension.Error) {
        console.log('Debug info: ' + JSON.stringify(error.debugInfo));
    }
});