Remove unused FunctionTypeImpl.relateX() methods.
Remove unused FunctionTypeImpl.relateX() methods.

Change-Id: I579dc738f00cd009c0089eb044b13c4541580465
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/217680
Reviewed-by: Brian Wilkerson <1f7641b6b14c52b9163524ab8d9aabff80176f21@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