message: ref(core): Remove unnecessary nested `dropUndefinedKeys` call
  remove an unnecessary nested call to dropUndefinedKeys which we don't need because the function is already recursive.
diff: @@ -136,12 +136,10 @@ function createEventEnvelopeHeaders(
  environment: event.environment,
  release: event.release,
  transaction: event.transaction,
  - user:
  - event.user &&
  - dropUndefinedKeys({
  + user: event.user && {
  id: event.user.id,
  segment: event.user.segment,
  - }),
  + },
  public_key: dsn.publicKey,
  }),
  }),
  