Remove redundant DotProtoNoPackage constructor in DotProtoPackageSpec

[riz0id]

DotProtoPackageSpec previously was equivalent to Maybe DotProtoIdentifier using the case where Nothing :: Maybe DotProtoIdentifier to denote a protobuf file without a package statement declaring the name of the package. This updates the definition of the DotProtoPackageSpec so that it only wraps the DotProtoIdentifier type:

newtype DotProtoPackageSpec = DotProtoPackageSpec 
  { getDotProtoPackageSpec :: DotProtoIdentifier }

This change removes the DotProtoNoPackage constructor and instead relies on the Anonymous constructor in DotProtoIdentifier to represent the case where no package is declared.