fix(reactive): delete useless code in function reactive

[lijingfaatcumt]

delete useless code in function reactive(#2951)
i think the code above i delete is useless, because in function createReactiveObject will solve the situation that if trying to observe a readonly proxy, return the readonly version, becasuse in createReactiveObject , except readonly() on a reactive object,
as long as the target is a proxy, the function createReactiveObject will return the target, so the code is repleat, and when i delete
the code above i mentioned, when i run 'npm test', it can pass and has no errors

[posva]

If you are submitting a fix, can you add a test that failed before and now passes?

[lijingfaatcumt]

If you are submitting a fix, can you add a test that failed before and now passes

@posva i only find 4 line code that i think they are useless, and i want to delete them, and when i delete them and run 'npm test', there are no errors, so i pull this request, then reason i think useless is bellow

if (
    target[ReactiveFlags.RAW] &&
    !(isReadonly && target[ReactiveFlags.IS_REACTIVE])
  ) {
    return target
  }

in function createReactiveObject can return the proxy if the target is a readonly proxy, so

//if trying to observe a readonly proxy, return the readonly version.
  if (target && (target as Target)[ReactiveFlags.IS_READONLY]) {
    return target
  }

in function reactive can deleted

[lijingfaatcumt]

If you are submitting a fix, can you add a test that failed before and now passes?

no, originally i want to mention a bug, but this is not a bug,so the bug i mentioned is closed