Revert class hoisting

Classes should not hoist

This is a revert of 8da94294ed279e60d05a9ff116de00b030d63897 and 5d8db529fe8cba856b3f174baa6a5082e396ad7b

Review URL: https://github.com/google/traceur-compiler/pull/460

Closes #460.
Add test with export * leading to duplicate export