Re-pack secondary dexes even if metadata isn't present
Re-pack secondary dexes even if metadata isn't present

Summary:
`metadata.txt` is FB-specific; we shouldn't bail on repacking when it's
not found.

Reviewed By: onomatopoeia, dariorussi

Differential Revision: D3975852

fbshipit-source-id: ece0358bf72a3d991c1fd530a3bfdd0c03ce8f90

facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex