Remove guard against @POST("")

An API I use does not follow standard REST conventions.  POST requests all go the same base endpoint and are differentiated with a field param.  The URL endpoint can not have an ending "/" or a 404 is thrown.  I removed the check and the test and 'mvn clean verfiy' ran fan.

http://api.foo.com/main => works
http://api.foo.com/main/ => 404