this answer can be confusing
do read the comments attached to this post and make sure this is what you are after
‘svn delete’ works against repository content, not against the repository itself. for doing repository maintenance (like completely deleting one) you should use svnadmin.
However, there’s a reason why svnadmin doesn’t have a ‘delete’ subcommand. You can just
rm -rf $REPOS_PATH
on the svn server,
where $REPOS_PATH is the path you used to create your repository with
svnadmin create $REPOS_PATH