Remove dead code related to function body dispatch

Remove dead code related to function body dispatch

Summary:
Removes:
- logic that emit function body dispatch
- logic that retranslates function body dispatch
- LdARNumParams IR opcode
- Func::getDVFunclets()

A minor modification was made to publishOptFuncCode():
- Func::getDVFunclets().size() == 0 was replaced with an equivalent logic
- a stronger SrcKey-based comparison is used to identify entry translation (it
  was not incorrect only by accident, as other ResumeModes are impossible at
  entry)

Reviewed By: oulgen

Differential Revision: D23416677

fbshipit-source-id: 22796ff44398837ded98acbe4e4f656ee8b97c9d