THRIFT-3869 Remove Dart packages during make clean
Client: Dart
Patch: Mark Erickson <mark.erickson@workiva.com>

This closes #1047
diff --git a/lib/dart/Makefile.am b/lib/dart/Makefile.am
index 6dfff40..a6e4556 100644
--- a/lib/dart/Makefile.am
+++ b/lib/dart/Makefile.am
@@ -22,5 +22,7 @@
 
 clean-local:
 	$(RM) -r .pub
+	find . -type d -name "packages" | xargs $(RM) -r
+	find . -type f -name ".packages" | xargs $(RM)
 
 check-local: all