Remove @required from AnalysisDriver packages parameter.
Remove @required from AnalysisDriver packages parameter.

It is required, and we really expect clients to provide it.
But this is a breaking change, and it causes internal build failures.

R=1f7641b6b14c52b9163524ab8d9aabff80176f21@google.com, 3faecbdd7b7be83f493f037bf1d597e6bb9d0848@google.com

Change-Id: I3afd8b748e41c5b4ac7a8e4ad4ac4aafc5a17204
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/135344
Reviewed-by: Brian Wilkerson <1f7641b6b14c52b9163524ab8d9aabff80176f21@google.com>
Reviewed-by: Phil Quitslund <3faecbdd7b7be83f493f037bf1d597e6bb9d0848@google.com>
Commit-Queue: Konstantin Shcheglov <09e4d7516628963212bf4aace2f97603d2b706e4@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk