[perl] Remove duplicate json and plaintext [ci skip] (TechEmpower#9898)

Author: joanhey

frameworks/Perl/feersum/benchmark_config.json

@@ -29,12 +29,10 @@
     },
     "mysql": {
       "dockerfile": "feersum.dockerfile",
-      "json_url": "/json",
       "db_url": "/db",
       "query_url": "/queries?queries=",
       "fortune_url": "/fortunes",
       "update_url": "/updates?queries=",
-      "plaintext_url": "/plaintext",
       "cached_query_url": "/cached-queries?count=",
       "port": 8080,
       "approach": "Realistic",