OK here we go.
Don't blame me if this breaks anything, it probably needs more testing:
Simply save as something like trim_drafts.php in your mu plugins folder:
<?php
function trim_revisions($post) {
global $wpdb;
$sql="delete from ".$wpdb->posts." where post_status='inherit' and (post_name like '".$post->ID."-autosave%' or post_name like '".$post->ID."-revision%')";
$wpdb->query($sql);
}
add_action('new_to_publish', 'trim_revisions');
add_action('pending_to_publish', 'trim_revisions');
add_action('draft_to_publish', 'trim_revisions');
add_action('private_to_publish', 'trim_revisions');
?>
Then if you are really confident, or mad you save the following in your top level directory as something like delete_stuff.php
<?php
require( dirname(__FILE__) . '/wp-config.php' );
global $wpdb;
$prefix="wp_";
$blog_list = $wpdb->get_results( "SELECT blog_id FROM " . $wpdb->blogs);
foreach ($blog_list as $bloglist) {
$sql="delete from ".$prefix.$bloglist->blog_id."_posts where post_status='inherit' and (post_name like '%autosave%' or post_name like '%revision%')";
$wpdb->query($sql);
}
?>
Then access it from your browser.
Dont forget to backup your DB first and to delete the file you created in the second part afterwards.