git-svn: remove any need for the XML::Simple dependency

git-svn: remove any need for the XML::Simple dependency

XML::Simple was originally required back when I made svn-arch-mirror
because I needed to explictly track renames with Arch.  Then I carried
it over to git-svn because I was afraid somebody could commit an svn
log message that could throw off a non-XML log parser.  Then I noticed
the <n> lines column in the header.  So, no more XML :)

Signed-off-by: Eric Wong <normalperson@yhbt.net>
Signed-off-by: Junio C Hamano <junkio@cox.net>