doc: remove em dashes

Our documentation uses em dashes inconsistently. They are treated
inconsistently typographically too. (For example, they are sometimes
surrounded by spaces and sometimes not.) They are also often confused
with ordinary hyphens such as in the CHANGELOG, where they are
inadvertently mixed together in a single list. The difference is
not obvious in the raw markdown but is very noticeable when rendered,
appearing to be a typographical error (which it in fact is).

The em dash is never needed. There are always alternatives. Remove em
dashes entirely.

PR-URL: https://github.com/nodejs/node/pull/32080
Backport-PR-URL: https://github.com/nodejs/node/pull/32149


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>