I also submitted this as a bug (since its about missing documentation).
This documentation does not mention the "svn_delete" command, but it was added in version 0.4. You can check the release notes here:
http://pecl.php.net/package/svn/0.4
Also, you could look at the contents of the current source code (svn-0.5.1/svn.c).
But what you really need to know is that the svn_delete command works correctly with this prototype:
svn_delete(string path [, bool force = true])
It returns true on success and false on failure.