Remove very wide `img` base style as it breaks existing page layouts.

Given a page with a picture with explicit size within it:

<img class="logo" src="https://cliketik.fr/themes/img/labels/logo_pnr.png" alt="marker" height="40px"/>

Before, an image with an explicit height would be displayed at its natural size.

Cf. broken pen

After the change, the image retains its explicit size:

Cf. expectation pen