Comment on Remove WordPress Meta Generator Tag by SEO Dave.
I don’t log into other users websites other than to try to fix issues with my own WordPress themes and then only on rare occasions (99% of the time the fixes are easy).
This is the exact code I use in the Stallion Responsive SEO theme package to remove Post Relational Links:
<?php remove_action('wp_head', 'adjacent_posts_rel_link_wp_head'); ?>
Looking through the code you originally posted could be the formatting, sometimes copying and pasting from one website and into a comment changes the ” and ‘ characters which breaks the code. The ‘ should be the character you should see on your keyboard under (same key) the @ sign.
I’ll update my comment above with code I know works (didn’t really look at the code, just copied yours) after sending this.