consensus: remove some unimplemented methods
consensus: remove some unimplemented methods

Change-Id: I82089fa5a4d1e62e63c2656cc6ffeefccf10376c
Reviewed-on: http://gerrit.cloudera.org:8080/4452
Reviewed-by: David Ribeiro Alves <78b9f953b197533e9b51c860b080869056433b48@apache.org>
Tested-by: Kudu Jenkins

cloudera/kudu,EvilMcJerkface/kudu,InspurUSA/kudu,InspurUSA/kudu,cloudera/kudu,cloudera/kudu,helifu/kudu,helifu/kudu,EvilMcJerkface/kudu,cloudera/kudu,cloudera/kudu,helifu/kudu,EvilMcJerkface/kudu,helifu/kudu,InspurUSA/kudu,helifu/kudu,andrwng/kudu,andrwng/kudu,EvilMcJerkface/kudu,andrwng/kudu,helifu/kudu,EvilMcJerkface/kudu,InspurUSA/kudu,cloudera/kudu,andrwng/kudu,InspurUSA/kudu,andrwng/kudu,InspurUSA/kudu,andrwng/kudu,helifu/kudu,helifu/kudu,EvilMcJerkface/kudu,andrwng/kudu,InspurUSA/kudu,InspurUSA/kudu,EvilMcJerkface/kudu,cloudera/kudu,EvilMcJerkface/kudu,andrwng/kudu,EvilMcJerkface/kudu,cloudera/kudu,InspurUSA/kudu,helifu/kudu,cloudera/kudu,andrwng/kudu