Remove normalize middleware

[teamon]

Tesla.Env should have a strict spec; adapters should conform to this spec.

• Make the Tesla.Adapter spec more strict
• Move the normalization logic into adapters
  • Update httpc adapter
  • Update hackney adapter
  • Update ibrowse adapter
• Remove raise in case of adapter error

It is possible that this is not a breaking change, but it might be, hence it is.