all: document legacy //go:linkname for final round of modules

all: document legacy //go:linkname for final round of modules

Add linknames for most modules with ≥50 dependents.
Add linknames for a few other modules that we know
are important but are below 50.

Remove linknames from badlinkname.go that do not merit
inclusion (very small number of dependents).
We can add them back later if the need arises.

Fixes #67401. (For now.)

Change-Id: I1e49fec0292265256044d64b1841d366c4106002
Reviewed-on: https://go-review.googlesource.com/c/go/+/587756
Auto-Submit: Russ Cox <rsc@golang.org>
TryBot-Bypass: Russ Cox <rsc@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>