Remove LOGLEVEL DB since is no longer used (#271)

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

Author: EdenGri

tests/mock_tables/asic0/database_config.json

@@ -22,11 +22,6 @@
             "separator": ":",
             "instance" : "redis"
         },
-        "LOGLEVEL_DB" : {
-            "id" : 3,
-            "separator": ":",
-            "instance" : "redis"
-        },
         "CONFIG_DB" : {
             "id" : 4,
             "separator": "|",

tests/mock_tables/asic1/database_config.json

@@ -22,11 +22,6 @@
             "separator": ":",
             "instance" : "redis"
         },
-        "LOGLEVEL_DB" : {
-            "id" : 3,
-            "separator": ":",
-            "instance" : "redis"
-        },
         "CONFIG_DB" : {
             "id" : 4,
             "separator": "|",

tests/mock_tables/asic2/database_config.json

@@ -22,11 +22,6 @@
             "separator": ":",
             "instance" : "redis"
         },
-        "LOGLEVEL_DB" : {
-            "id" : 3,
-            "separator": ":",
-            "instance" : "redis"
-        },
         "CONFIG_DB" : {
             "id" : 4,
             "separator": "|",

tests/mock_tables/database_config.json

@@ -22,11 +22,6 @@
             "separator": ":",
             "instance" : "redis"
         },
-        "LOGLEVEL_DB" : {
-            "id" : 3,
-            "separator": ":",
-            "instance" : "redis"
-        },
         "CONFIG_DB" : {
             "id" : 4,
             "separator": "|",

tests/mock_tables/global_db/database_config.json

@@ -22,11 +22,6 @@
             "separator": ":",
             "instance" : "redis"
         },
-        "LOGLEVEL_DB" : {
-            "id" : 3,
-            "separator": ":",
-            "instance" : "redis"
-        },
         "CONFIG_DB" : {
             "id" : 4,
             "separator": "|",