sed(1): Revert r303047 "cleanup" and therefore r303572.

While big, the change was meant to have no effect on behavior and instead
so far we have found two regressions: one in the etcupdate tests and
another one in the games/openttd port[1].

Revert to a known working state. We will likely have to split the patch in
functional parts before bringing back the changes.

PR: 195929
Reported by: danfe, madpilot [1]