arch: powerpc: defconfig: Drop obsolete CONFIG_NET_CLS_TCINDEX

This option was removed from the Kconfig in commit
8c710f75 ("net/sched: Retire tcindex classifier") but it was not
removed from the defconfigs.

Fixes: 8c710f75 ("net/sched: Retire tcindex classifier")
Signed-off-by: Johan Korsnes <johan.korsnes@gmail.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20250323191116.113482-1-johan.korsnes@gmail.com