Using abandoned QR code generator

[MakisH]

We are currently prepending a QR code on every printed page, but the service no longer exists:

precice.github.io/_includes/head.html

Lines 93 to 102 in da79df0

	<!-- QR code to retrieve printed page -->
	<style>
	@media print {
	div.post-header:before {
	content: url('https://chart.googleapis.com/chart?cht=qr&chs=100x100&chl=https://precice.org{{page.url}}&choe=UTF-8');
	margin-top: -25px;
	float: right;
	}
	}
	</style>

This is also being reported in a dead URL checker, polluting the actual results.

Discussion and some alternatives: https://stackoverflow.com/q/77757225/2254346