t9120: don't expect failure with SVN_HTTPD_PORT unset

t9120: don't expect failure with SVN_HTTPD_PORT unset

The test still passes when SVN_HTTPD_PORT is not set. Futhermore, t9115
and t9118 don't check if SVN_HTTPD_PORT is set even though they both use
start_httpd() from lib-git-svn.sh. Admittedly, the test is not very
meaningful without SVN_HTTPD_PORT, as commit f5530b (support for funky
branch and project names over HTTP(S) 2007-11-11) states that the URI
escaping is only done over HTTP(S).

Signed-off-by: Stephen Boyd <bebarino@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>