remove get_server_date from tests
remove get_server_date from tests

Jenkins doesn't seem to return the 'Date' in the header
anymore. For now, just remove the test that checks for
the Date. The functionality can be removed later.

pc-rhuang/jenkins_api_client,Tyrael/jenkins_api_client,Tyrael/jenkins_api_client,yp-engineering/jenkins_api_client,arangamani/jenkins_api_client,stjohnjohnson/jenkins_api_client,cocktail-io/jenkins_api_client,cocktail-io/jenkins_api_client,pac78275/jenkins_api_client,mattrose/jenkins_api_client,attilastrba/jenkins_api_client,mattrose/jenkins_api_client,pac78275/jenkins_api_client,pc-rhuang/jenkins_api_client,stjohnjohnson/jenkins_api_client,VodafoneAustralia/vha-jenkins-api-client,yp-engineering/jenkins_api_client,attilastrba/jenkins_api_client,VodafoneAustralia/vha-jenkins-api-client,arangamani/jenkins_api_client