ThemeBoy

Local Open Sans contains copies of Open Sans fonts that WordPress loads from Google Fonts. The plugin deregisters the admin style that loads these fonts remotely and replaces it with a stylesheet that loads local copies of the same fonts.
Recommended for development when “fonts.googleapis.com” is adding time to admin pageloads. Not recommended for production (live sites) because it is almost always faster for your visitors to load fonts from Google or to use cached copies.

Local Open Sans

Replace Open Sans with a local copy to speed up admin testing and development.

suifengtec

Remove Google fonts link from WP core( old versions ) and default themes:: twentyfourteen,twentyfifteen,twentysixteen,twentyseventeen.
<ul>
<li>Remove Open Sans font Link from WP core</li>
<li>Remove Lato font Link from the WP default theme <code>twentyfourteen</code>.</li>
<li>Remove Noto Sans font link,Noto Serif font link,Inconsolata font link from the WP default theme <code>twentyfifteen</code>.</li>
<li>Remove Noto Serif font link,Inconsolata font link from the WP default theme <code>twentyfifteen</code>.</li>
<li>Remove Inconsolata font link from the WP default theme <code>twentyfifteen</code>.</li>
<li>Remove Merriweather font link from the WP default theme <code>twentysixteen</code>.</li>
<li>Remove Montserrat font link from the WP default theme <code>twentysixteen</code>.</li>
<li>Remove Inconsolata font link from the WP default theme <code>twentysixteen</code>.</li>
<li>Remove Libre Franklin font link from the WP default theme <code>twentyseventeen</code>.</li>
</ul>

Remove  Google Fonts

now the default font in the back end is sans-serif. It's fine for me as it's not for the viewers.



works perfectly even for current wordpress version

Remove Google fonts link from WP core and default themes.

Local Open Sans vs Remove Google Fonts