Drop pkg/diagnostics from .packages

Follow-up on https://dart-review.googlesource.com/c/sdk/+/233448

Change-Id: I8f30ff6c2f2bb6b6818815592cd7c52c2c41c143
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/233501
Auto-Submit: Kevin Moore <kevmoo@google.com>
Commit-Queue: Kevin Moore <kevmoo@google.com>
Reviewed-by: Devon Carew <devoncarew@google.com>
Commit-Queue: Devon Carew <devoncarew@google.com>
diff --git a/.packages b/.packages
index 76b0165..822b3c3 100644
--- a/.packages
+++ b/.packages
@@ -42,7 +42,6 @@
 dds_service_extensions:pkg/dds_service_extensions/lib
 dev_compiler:pkg/dev_compiler/lib
 devtools_shared:third_party/devtools/devtools_shared/lib
-diagnostic:pkg/diagnostic/lib
 expect:pkg/expect/lib
 ffi:third_party/pkg/ffi/lib
 fixnum:third_party/pkg/fixnum/lib