clean up default type mapping (#11336)

Author: wing328

modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java

@@ -1595,8 +1595,6 @@ public DefaultCodegen() {
         typeMapping.put("array", "List");
         typeMapping.put("set", "Set");
         typeMapping.put("map", "Map");
-        typeMapping.put("List", "List");
-        typeMapping.put("Set", "Set");
         typeMapping.put("boolean", "Boolean");
         typeMapping.put("string", "String");
         typeMapping.put("int", "Integer");