renumber_registers should create and clear cfg only when editable cfg doesn't exist
renumber_registers should create and clear cfg only when editable cfg doesn't exist

Summary: as in title

Reviewed By: justinjhendrick

Differential Revision: D15265239

fbshipit-source-id: 717c26a0f3b556d161bad08bc9d8c5540f9c14c5

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