Remove format.atom check.

The check was added at
https://github.com/rubygems/rubygems.org/commit/3d0c24e27ada9989a252e998c19d623d1307e1a2#diff-e4663ec6bcde373fc1ee998eb69725b1R3
Commit message says it was added to make clearance happy, however we
dont need that check anymore.
Merge pull request #804 from arthurnn/remove_atom_check

Remove format.atom check.