vim: use upstream generated .po files

vim: use upstream generated .po files

A previous commit attempted to fix reproducibility errors by forcing
regeneration of .po files. Unfortunately this triggered a different
type of reproducibility issue.

Work around this by adjusting the timestamps of the troublesome .po
files so they are not regenerated and we use the shipped upstream
versions of the files.

The shipped version of ru.cp1251.po doesn't seem to have been created
with the vim tooling and specifies CP1251 instead of cp1251, fix that.

Signed-off-by: Steve Sakoman <steve@sakoman.com>