Remove a FIXME and comment that is simply no longer true

Author: DougGregor

include/swift/AST/ProtocolConformance.h

@@ -444,11 +444,6 @@ class NormalProtocolConformance : public ProtocolConformance,
                            LazyResolver *resolver = nullptr) const;
 
   /// Retrieve the value witness corresponding to the given requirement.
-  ///
-  /// Note that a generic witness will only be specialized if the conformance
-  /// came from the current file.
-  ///
-  /// FIXME: The 'only specialized if from the same file' bit is awful.
   Witness getWitness(ValueDecl *requirement, LazyResolver *resolver) const;
 
   /// Determine whether the protocol conformance has a witness for the given