fix removeReplicaByZKPath

fix bug: add zkpath empty judge

fix: rewrite code

delete useless code.

fix:ast fromat

fix bug

add test_drop_replica

add drop_replica doc

add drop databse checkAccess

refactor dropReplica

update tests

add static method StorageReplicatedMergeTree::dropReplicaByZkPath

update doc and delete useless code

fix conflict

fix doc

fix doc

fix StorageReplicatedMergeTree::dropReplica

fix bug

delete useless code