Remove LOGLEVEL DB since is no longer used (sonic-net#2507)

This PR is part of the following HLD:
Persistent loglevel HLD: sonic-net/SONiC#1041

- What I did
Deleted the LOGLEVEL_DB.
After the Logger tables moved from the LOGLEVEL_DB to the CONFIG_DB and the jinja2_cache was deleted the LOGLEVEL_DB is not in use.

- How I did it
Removed the LOGLEVEL_DB from the SONiC code

- How to verify it
All tests were passed

fdbsyncd/fdbsyncd.cpp

@@ -19,7 +19,6 @@ int main(int argc, char **argv)
     DBConnector appDb(APPL_DB, DBConnector::DEFAULT_UNIXSOCKET, 0);
     RedisPipeline pipelineAppDB(&appDb);
     DBConnector stateDb(STATE_DB, DBConnector::DEFAULT_UNIXSOCKET, 0);
-    DBConnector log_db(LOGLEVEL_DB, DBConnector::DEFAULT_UNIXSOCKET, 0);
     DBConnector config_db(CONFIG_DB, DBConnector::DEFAULT_UNIXSOCKET, 0);
 
     FdbSync sync(&pipelineAppDB, &stateDb, &config_db);

tests/mock_tests/database_config.json

@@ -27,11 +27,6 @@
             "separator": ":",
             "instance" : "redis"
         },
-        "LOGLEVEL_DB" : {
-            "id" : 3,
-            "separator": ":",
-            "instance" : "redis"
-        },
         "CONFIG_DB" : {
             "id" : 4,
             "separator": "|",