apache: re-add Content-Encoding=gzip to .gz files

this will make them displayed in browsers, etc
Also, drop the auto-inflate thing, that causes apt and clients that
actually expects compressed content to blow up (and we really shouldn't
decompress silently anyway: if we say we are encoding in gzip we should
serve stuff encoded with gz.

AddEncoding seems to do something more than just add the
Content-Encoding header, as client not specifing Accept-Encoding=gzip
would fail with 406.  Let's just add the single header manually for now.

Signed-off-by: Mattia Rizzolo <mattia@debian.org>