You can create a page without the featured image by doing the following:
1) Create a page with the ‘Page (alternative)’ template. See screenshot:
Know the ID of that page. You’ll need it in step 2. The id can be seen in your browser’s address bar while you are in the edit page screen. See screenshot:
2) Install the Simple Custom CSS plugin. Once you install and activate it, in your Admin Panel please go to ‘Appearance’ > ‘Custom CSS’. There insert the code you see below. However instead of 638 use the id of the page you want no header image on.