nodes and audit_history tables
This PR removes all code reference to audit_histories table and
```
audit_reputation_alpha, audit_reputation_beta,
unknown_audit_reputation_alpha, unknown_audit_reputation_beta,
```
columns from nodes table.
It also drops audit_histories table from the db since the code
that's referencing it currently are not being used.
Change-Id: Ifcda8db36afb3a333d487ff831f2fdefc8b02a4c
