fix(mailcard): Remove CSS before PDF conversion (refs #4428)

The initial problem was triggered by the string "<https://...>" appearing in a
CSS comment. As html2ps do not interpret the CSS rules in the HTML document, we
can completly remove "<style>...</style>" strings from the HTML.
Merge pull request #1057 from eguaj/3.1-A4428

fix(mailcard): Remove CSS before PDF conversion (fixes #4428)