Removed useless :lang option.

Rails4 RP #2104.

https://github.com/opf/openproject/commit/4f9b6d81f4c2108ca48cf07909f50628507ee453

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extra : convert_revision : svn%3Ae93f8b46-1217-0410-a6f0-8f06a7374b81/trunk%407902