In FF58: datareporting.healthreport.service.enabled does not exist in about:config and datareporting.healthreport.uploadEnabled is true by default.
After going to Help->Health Report and turning off data sharing, datareporting.healthreport.uploadEnabled is set to false as expected. In FF52 Same as FF58, service.enabled is missing and upload enabled is true by default. After going to Preferences->Advanced->Data Choices and deselecting "Enable Firefox Health Report" upload.enabled is set to false as expected.
