Используйте Regex
console.log( x.replace(/( |<([^>]+)>)/ig, "") );
var x = `{ \n \"formType\":\"CreateCaseRequest\",\n \"documentID\":270550224,\n \"documentRev\":\"1\",\n \"formVersion\":\"v1\",\n \"createdDateTime\":\"2019-03-25T13:31:44.216+0000\",\n \"documentStatus\":\"Draft\",\n \"documentTitle\":\n {\n },\n \"documentSynopsis\":\n {\n },\n \"highPriority\":false,\n }`
console.log( x.replace(/( |<([^>]+)>)/ig, "") );