[intro.memory] Remove stray bit definitions

[Eisenwave]

This old paragraph defines two terms which aren't used anywhere else in the document. Maybe they have been used historically and someone forgot to remove them, or maybe they haven't ever been used.

On a personal note, I also have to say that I have never heard someone say high-order bit or low-order bit. The terminology least significant and most significant is much more popular in my experience, self-explanatory, and used in other places in the C++ standard.

[AlisdairM]

I have grepped all the .tex files to confirm that these definitions are the only occurrences of "high-order" and "low order" in the standard. To double-check, I verified that are no occurrences of "high order" nor "low order" either.

[jensmaurer]

I've confirmed the definitions are unused by searching through the PDF. This is ancient goo that should go.