git-svn: remove non-delta fetch code paths

git-svn: remove non-delta fetch code paths

We have less code to worry about now.  As a bonus, --revision
can be used to reliably skip parts of history whenever fetch is
run, not just the first time.  I'm not sure why anybody would
want to skip history in the middle, however...

For people (nearly everyone at the moment) without the
do_switch() function in their Perl SVN library, the entire tree
must be refetched if --follow-parent is used and a parent is
found.  Future versions of SVN will have a working do_switch()
function accessible via Perl.

Accessing repositories on the local machine (especially file://
ones) is also slightly slower as a result; but I suspect most
git-svn users will be using it to access remote repositories.

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