Stop manually handling broken symlinks in listDir in pub.
Stop manually handling broken symlinks in listDir in pub.

Review URL: https://codereview.chromium.org//14187003

git-svn-id: a962b240025cf0577aa172e20f49ccb159ba6be1@21529 260f80e4-7a28-3924-810f-c04153c831b5

maxwellpeterson-wf/pub,dart-lang/pub,dart-lang/pub,cjkao/dart-pub,computmaxer/pub