changing charset configuration in all templates to simpler equivalent

[jonashamm]

Same as my two last pull requests, just … in master branch According to the W3C the previous line does exactly the same as this new, more readable, line. https://www.w3.org/International/questions/qa-html-encoding-declarations

Sorry, I don't know why "wire/modules/Markup/MarkupHTMLPurifier/htmlpurifier/HTMLPurifier.standalone.php" shows so many changes, while I changed just one line. Maybe you can exclude this while merging?