Remove IfConfigDecl from the AST

The swift-syntax tree retains information about the parsed #if
regions. Drop it from the semantic AST.

lib/Parse/ParseIfConfig.cpp

@@ -990,7 +990,7 @@ ParserStatus Parser::parseIfConfig(
     });
 }
 
-ParserStatus Parser::parseIfConfigDeclAttributes(
+ParserStatus Parser::parseIfConfigAttributes(
     DeclAttributes &attributes, bool ifConfigsAreDeclAttrs,
     PatternBindingInitializer *initContext) {
   ParserStatus status = makeParserSuccess();