I just did an Grid Infrastructure Update to Oracle 12.2 with the latest PSU Aug 2017.
I did my preparation with the help of the Doc ID 2111010.1
„12.2 Grid Infrastructure and Database Upgrade steps for Exadata Database Machine running 22.214.171.124 and later on Oracle Linux“
In the Post-upgrade Steps was written that the Management DB should be deconfigured
- Deconfigure MGMTDB
The deconfigure is obsolete and the MGMTDB is now part of the Update.
Here the original text from the Doc ID.
For me it looks like that the revision of the document is not yet finished
So if you plan a Grid Upgrade in the near future read the document very carefully and if needed open an SR