Historically, it’s been impossible to make these things disappear as they are user settings and not considered part of the page you have control over.
However, as of 2017, the @page at-rule has been standardized, which can be used to hide the page title and date in modern browsers:
@page { size: auto; margin: 0mm; }
Print headers/footers and print margins
When printing Web documents, margins are set in the browser’s Page Setup (or Print Setup) dialog box. These margin settings, although set within the browser, are controlled at the operating system/printer driver level and are not controllable at the HTML/CSS/DOM level. (For CSS-controlled printed page headers and footers see Printing Headers .)
The settings must be big enough to encompass the printer’s physical non-printing areas. Further, they must be big enough to encompass the header and footer that the browser is usually configured to print (typically the page title, page number, URL and date). Note that these headers and footers, although specified by the browser and usually configurable through user preferences, are not part of the Web page itself and therefore are not controllable by CSS. In CSS terms, they fall outside the Page Box CSS2.1 Section 13.2.
… i.e. setting a margin of 0 hides the page title because the title is printed in the margin.
Credit to Vigneswaran S for this tip.