Remove co19 hack from part multi-use check.

Change-Id: I3b93d7c84f48730c570cffa7d508c9194508f1b2
Reviewed-on: https://dart-review.googlesource.com/60561
Reviewed-by: Kevin Millikin <kmillikin@google.com>
Commit-Queue: Aske Simon Christensen <askesc@google.com>
diff --git a/pkg/front_end/lib/src/fasta/source/source_library_builder.dart b/pkg/front_end/lib/src/fasta/source/source_library_builder.dart
index 7342f1c..1529ed0 100644
--- a/pkg/front_end/lib/src/fasta/source/source_library_builder.dart
+++ b/pkg/front_end/lib/src/fasta/source/source_library_builder.dart
@@ -600,9 +600,7 @@
       if (part == this) {
         addCompileTimeError(messagePartOfSelf, -1, noLength, fileUri);
       } else if (seenParts.add(part.fileUri)) {
-        if (part.partOfLibrary != null &&
-            // TODO(askesc): Remove this hack when co19 fix is rolled in.
-            !part.fileUri.path.endsWith("/co19/src/Utils/expect_common.dart")) {
+        if (part.partOfLibrary != null) {
           addProblem(messagePartOfTwoLibraries, -1, noLength, part.fileUri,
               context: [
                 messagePartOfTwoLibrariesContext.withLocation(