Summary: When running with node 8, the babel plugins `async-to-generator` and `syntax-trailing-function-commas` are unnecessary. Removing them makes runtime transpilation faster, and the resulting code is closer to the original (useful with debugging: less unmapped code areas, better breakpoint support, less renamed variables).
Reviewed By: mjesun
Differential Revision: D5842305
fbshipit-source-id: d99f719794e4a8f48fd10b0349fbb36f2994666e