fdo#39468 Translate German comments (include/filter/msfilter/svdfppt.hxx)

Translate remaining German comments to English.
Also remove an empty comment.

Change-Id: I11b8fad73a7a7e9bfc751d812be05d4b81784fbb
Reviewed-on: https://gerrit.libreoffice.org/7666
Reviewed-by: Norbert Thiebaud <nthiebaud@gmail.com>
Tested-by: Norbert Thiebaud <nthiebaud@gmail.com>