WordPress: Remove Shortcake Add Post Element button

admin.css

// Globally hide the TinyMCE media buttons so that we can alter them and show them
// once updated.
.wp-media-buttons {
  display: none;
}

updateMediaButtons.js

/**
 * Update the media buttons.
 */
function updateMediaButtons() {
  // Update the Add Media button text.
  const addMediaButton = document.querySelectorAll('.insert-media.add_media');

  if (addMediaButton) {
    Array.prototype.forEach.call(addMediaButton, (button) => {
      const newButton = button;

      // Get the icon.
      const addMediaButtonIcon = newButton.querySelector('span');
      let newText = 'Add Media or Post Element';
      if (addMediaButtonIcon) {
        newText = addMediaButtonIcon.outerHTML + newText;
      }
      newButton.innerHTML = newText;
    });
  }

  // Show the media buttons.
  const mediaButtons = document.querySelectorAll('.wp-media-buttons');

  if (mediaButtons) {
    Array.prototype.forEach.call(mediaButtons, (buttons) => {
      const newButtons = buttons;

      newButtons.style.display = 'block';
    });
  }
}

updateMediaButtons();