By default, the following tag shows up in every WordPress install.
<link rel="wlwmanifest" type="application/wlwmanifest+xml" href="https://yourdomain.com/wp-includes/wlwmanifest.xml" />
The above link is actually used by Windows Live Writer. If you don’t know use Windows Live Writer, which we are guessing you don’t, this is just unnecessary code.
You can easily remove this in the perfmatters plugin by enabling the “Remove wlwmanifest Link” option.