Revert "(De-)serialization for foreign error conventions."

This reverts commit r27290 due to several test failures in SourceKit.

Swift SVN r27291

include/swift/Serialization/ModuleFormat.h

@@ -51,7 +51,7 @@ const uint16_t VERSION_MAJOR = 0;
 /// To ensure that two separate changes don't silently get merged into one
 /// in source control, you should also update the comment to briefly
 /// describe what change you made.
-const uint16_t VERSION_MINOR = 192; // Last change: foreign error convention
+const uint16_t VERSION_MINOR = 191; // Last change: consolidate function type representations
 
 using DeclID = Fixnum<31>;
 using DeclIDField = BCFixed<31>;
@@ -115,15 +115,6 @@ enum class FunctionTypeRepresentation : uint8_t {
 };
 using FunctionTypeRepresentationField = BCFixed<4>;
 
-enum class ForeignErrorConventionKind : uint8_t {
-  ZeroResult,
-  NonZeroResult,
-  NilResult,
-  NonNilError,
-};
-
-using ForeignErrorConventionKindField = BCFixed<2>;
-
 // These IDs must \em not be renumbered or reordered without incrementing
 // VERSION_MAJOR.
 enum class SILFunctionTypeRepresentation : uint8_t {
@@ -1209,15 +1200,6 @@ namespace decls_block {
     BCFixed<1> // is a decl
   >;
 
-  using ForeignErrorConventionLayout = BCRecordLayout<
-    FOREIGN_ERROR_CONVENTION,
-    ForeignErrorConventionKindField,  // kind
-    BCFixed<1>,                       // owned
-    BCVBR<4>,                         // error parameter index
-    TypeIDField,                      // error parameter type
-    TypeIDField                       // result type
-  >;
-
   using AbstractClosureExprLayout = BCRecordLayout<
     ABSTRACT_CLOSURE_EXPR_CONTEXT,
     TypeIDField, // type