CNDB-14848 CC5 remove unused duplicated constants from SchemaConstants (#1891)

### What is the issue
Fixes CNDB-14848, removing unused, duplicated constants from
`SchemaConstants`

### What does this PR fix and why was it fixed
`SchemaConstants` contains unused and duplicated constants left over
from previous rebases.

Author: djatnieks

src/java/org/apache/cassandra/schema/SchemaConstants.java

@@ -51,8 +51,6 @@ public final class SchemaConstants
     public static final String VIRTUAL_SCHEMA = "system_virtual_schema";
 
     public static final String VIRTUAL_VIEWS = "system_views";
-    public static final String SCHEMA_VIRTUAL_KEYSPACE_NAME = "system_virtual_schema";
-    public static final String SYSTEM_VIEWS_KEYSPACE_NAME = "system_views";
 
     public static final String DUMMY_KEYSPACE_OR_TABLE_NAME = "--dummy--";
 
@@ -66,9 +64,6 @@ public final class SchemaConstants
     /* replicate system keyspace names (the ones with a "true" replication strategy) */
     public static final Set<String> REPLICATED_SYSTEM_KEYSPACE_NAMES = ImmutableSet.of(TRACE_KEYSPACE_NAME, AUTH_KEYSPACE_NAME, DISTRIBUTED_KEYSPACE_NAME);
 
-    /* virtual keyspace names */
-    public static final Set<String> VIRTUAL_KEYSPACE_NAMES = ImmutableSet.of(SCHEMA_VIRTUAL_KEYSPACE_NAME, SYSTEM_VIEWS_KEYSPACE_NAME);
-
     /**
      * Longest acceptable file name. Longer names lead to file write or read errors.
      */
@@ -225,19 +220,10 @@ public static Set<String> getLocalAndReplicatedSystemTableNames()
                            .build();
     }
 
-    /**
-     * @return whether or not the keyspace is a virtual keyspace (system_virtual_schema, system_views)
-     */
-    public static boolean isVirtualKeyspace(String keyspaceName)
-    {
-        return VIRTUAL_KEYSPACE_NAMES.contains(keyspaceName.toLowerCase());
-    }
-
     public static boolean isInternalKeyspace(String keyspaceName)
     {
         return isLocalSystemKeyspace(keyspaceName)
-               || isReplicatedSystemKeyspace(keyspaceName)
-               || isVirtualKeyspace(keyspaceName);
+               || isReplicatedSystemKeyspace(keyspaceName);
     }
 
     /**