Cleanup layoutManager null-check when AbstractZkLedgerManagerFactory#newLedgerManagerFactory

[AnonHxy]

Descriptions of the changes in this PR:

Motivation

Remove the null-check from AbstractZkLedgerManagerFactory#newLedgerManagerFactory. The reason is that:

1. the parameter layoutManager in newLedgerManagerFactory() method can never be null. So this check is unnecessory
2. If the layoutManager is null and we return new FlatLedgerManagerFactory().initialize(conf, null, FlatLedgerManagerFactory.CUR_VERSION), the 'zk' in FlatLedgerManagerFactory is null and could throw NPE when invoke the methods in the FlatLedgerManagerFactory.

Changes

1. Cleanup layoutManager null-check when newLedgerManagerFactory()
2. Let layoutManager could never be null in FlatLedgerManagerFactory

[AnonHxy]

rerun failure checks

[AnonHxy]

rerun failure checks

[AnonHxy]

rerun failure checks

[AnonHxy]

rerun failure checks