build failure --without-ssl

[Eray Aslan]

dovecot-2.2.26.0:
$ ./configure --without-ssl && make
[...]
libtool:   error: cannot find the library
'../lib-ssl-iostream/libssl_iostream_openssl.la' or unhandled argument
'../lib-ssl-iostream/libssl_iostream_openssl.la'
make[3]: *** [Makefile:738: test-http-client] Error 1

Had a quick look.  When configured without ssl, the tests were failing
at run time for dovecot-2.2.25.  So, this change is good but not enough.
Apparently, some people do use dovecot without ssl.

https://bugs.gentoo.org/show_bug.cgi?id=599024

-- 
Eray