Two spaces after a period was an affectation of typewriters that used mono-spaced fonts. It was NEVER a practice of good typography.
In the early days of computer-based desktop publishing, I read an admonition in a font package I purchased to drop the two spaces after a period (and to use "smart quotes", etc.) around 1985 or so. So, yeah, it should be well and fully dead by now but isn't.
Now that we've matriculated to the HTML-driven world, the gods of rendering forgive us our sins because the HTML "rules" say that extra spaces are to be disregarded. The problem has "gone away" because the computer machines are smart enough to ignore our mistakes (at least in this one way).