[llvm-branch-commits] [BFI] Drop AllowSynthetic Parameter (PR #204767)

[Aiden Grossman via llvm-branch-commits]

https://github.com/boomanaiden154 created https://github.com/llvm/llvm-project/pull/204767

This was never set anywhere to something other than the default outside
of the implementation and synthetic profile counts are slated for
removal.