Remove deprecated warning in synthetic def

[changvvb]

Fixes #11022

[bishabosha]

Thank you for opening this PR, I will link to this comment on why we need to be careful with ignoring synthetic defs which I see you already protect against some cases: #10996 (comment)

[changvvb]

Thank you for opening this PR, I will link to this comment on why we need to be careful with ignoring synthetic defs which I see you already protect against some cases: #10996 (comment)

@bishabosha I want to know some cases that we should warn in synthetic scope

[smarter]

I want to know some cases that we should warn in synthetic scope

I mentioned some cases in #10996 (comment), as far as I can tell this PR has the same issues as #10996 and should be rejected for the same reason in favor of what I suggested in #10996 (comment)

[changvvb]

I checked these cases and got the following results:

@deprecated("no CaseClass", "0.1") case class CaseClass(rgb: Int)

object Test {

  abstract class TestX

  val x = new TestX {
    val obj = new CaseClass(5) // warn
  }

  val y = Option(5).map(new CaseClass(_)) // warn
  val z = CaseClass(4)  // not warn but seems not related with this PR
}

But I agree that should not check synthetic flag only.

[changvvb]

@bishabosha @smarter Is it possible to check the sourcePos of ctx owners? we can check whether exists owner sourcePos that

1. is not <no position>
2. is not sourcePos of the deprecated symbol.

I think the user code must have a valid sourcePos right?

[changvvb]

@bishabosha @smarter Is it possible to check the sourcePos of ctx owners? we can check whether exists owner sourcePos that

1. is not <no position>
2. is not sourcePos of the deprecated symbol.

I think the user code must have a valid sourcePos right?

This is not a good solution because should disable not only deprecated warnings but also other warnings in synthetic scope.