ObjC: Preserve unknown fields in proto3 syntax files.

As announced: https://groups.google.com/forum/#!topic/protobuf/VX5qEmTW3y0

The ObjC side of https://github.com/google/protobuf/issues/272

objectivec/GPBDescriptor_PackagePrivate.h

@@ -286,10 +286,6 @@ uint32_t GPBFieldTag(GPBFieldDescriptor *self);
 // would be the wire type for packed.
 uint32_t GPBFieldAlternateTag(GPBFieldDescriptor *self);
 
-GPB_INLINE BOOL GPBPreserveUnknownFields(GPBFileSyntax syntax) {
-  return syntax != GPBFileSyntaxProto3;
-}
-
 GPB_INLINE BOOL GPBHasPreservingUnknownEnumSemantics(GPBFileSyntax syntax) {
   return syntax == GPBFileSyntaxProto3;
 }

objectivec/GPBMessage.m

@@ -2372,17 +2372,11 @@ static void MergeRepeatedNotPackedFieldFromCodedInputStream(
         // zero signals EOF / limit reached
         return;
       } else {
-        if (GPBPreserveUnknownFields(syntax)) {
-          if (![self parseUnknownField:input
-                     extensionRegistry:extensionRegistry
-                                   tag:tag]) {
-            // it's an endgroup tag
-            return;
-          }
-        } else {
-          if (![input skipField:tag]) {
-            return;
-          }
+        if (![self parseUnknownField:input
+                   extensionRegistry:extensionRegistry
+                                 tag:tag]) {
+          // it's an endgroup tag
+          return;
         }
       }
     }  // if(!merged)

objectivec/Tests/GPBMessageTests+Serialization.m

@@ -113,35 +113,6 @@ static NSData *DataFromCStr(const char *str) {
   [msg release];
 }
 
-- (void)testProto3DroppingUnknownFields {
-  DropUnknownsFooWithExtraFields *fooWithExtras =
-      [[DropUnknownsFooWithExtraFields alloc] init];
-
-  fooWithExtras.int32Value = 1;
-  fooWithExtras.enumValue = DropUnknownsFooWithExtraFields_NestedEnum_Baz;
-  fooWithExtras.extraInt32Value = 2;
-
-  NSData *data = [fooWithExtras data];
-  XCTAssertNotNil(data);
-  DropUnknownsFoo *foo = [DropUnknownsFoo parseFromData:data error:NULL];
-
-  XCTAssertEqual(foo.int32Value, 1);
-  XCTAssertEqual(foo.enumValue, DropUnknownsFoo_NestedEnum_Baz);
-  // Nothing should end up in the unknowns.
-  XCTAssertEqual([foo.unknownFields countOfFields], 0U);
-
-  [fooWithExtras release];
-  data = [foo data];
-  fooWithExtras =
-      [DropUnknownsFooWithExtraFields parseFromData:data error:NULL];
-  XCTAssertEqual(fooWithExtras.int32Value, 1);
-  XCTAssertEqual(fooWithExtras.enumValue,
-                 DropUnknownsFooWithExtraFields_NestedEnum_Baz);
-  // And the extra value is gone (back to the default).
-  XCTAssertEqual(fooWithExtras.extraInt32Value, 0);
-  XCTAssertEqual([foo.unknownFields countOfFields], 0U);
-}
-
 - (void)testProto2UnknownEnumToUnknownField {
   Message3 *orig = [[Message3 alloc] init];