Fix index name case sensitivity as per Origin commit 68be72f ("Fix
case-sensitivity of index name on CREATE/DROP INDEX") which addressed
CASSANDRA-8365.
The grammar rules were imported from the following Origin commit:
ebc50d783505854f04f183297ad3009b9095b07e
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>