Free memory of ```mappedVars``` on the Python server side.
function freeMemory (mappedVars /*: Array<SublimeObject>*/, step /*: ?StepObject*/) /*: Promise<any> | void*/ {
  if (mappedVars.length > 0) {
    let mappedVarsStringify = []
    for (let mappedVar /*: Object*/ of mappedVars) {
      if (mappedVar.hasOwnProperty("self") && mappedVar.self) {
        delete mappedVar.self.code
        mappedVarsStringify.push(JSON.stringify(mappedVar.self))
      }
    }
    return simpleEval(`freeMemory(json.loads("""[${mappedVarsStringify.join(',')}]"""))`, false, step)
  }
}