Now, this link may be put there by your theme or by some plugin. Since you don’t give any link to your site and don’t tell me what theme you’re using, I can’t give you any more detailed hints on this.

Possible ways to fix this:
1. Find out which template file is guilty sending out these links, set up a child theme and put a copy of this file in the child theme, after having changed http to https.
2. It might be possible to fix this by installing the plugin really-simple-ssl
I’m not sure, but you may try. This plugin will try to change all on-site links to https.
3. Your theme might allow you to turn OFF these links. If that’s the case, then you could simply add them semi-manually, say with a plugin that will inject things you need inside the head tags.

Good luck. Let me know how you get along.