pkg/math: remove placeholder

R=sethladd@google.com

Review URL: https://codereview.chromium.org//541523002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@39946 260f80e4-7a28-3924-810f-c04153c831b5
fix build of try.dart

TBR

Review URL: https://codereview.chromium.org//546253002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@39947 260f80e4-7a28-3924-810f-c04153c831b5