[Enterprise InfluxDB] Remove other 1.2-specific mentions

[rkuchan]

The Enterprise InfluxDB docs contain unnecessary 1.2-specific content:

• In /guides/backup-and-restore/, remove the five warnings about versions 1.2.0 and 1.2.1. They start with In versions 1.2.0 and 1.2.1.
• In /troubleshooting/frequently_asked_questions/, remove the three known issues - they were all fixed in v1.2.5.
• In /troubleshooting/frequently_asked_questions/, remove the two warnings about versions 1.2.0 and 1.2.1. They start with In versions 1.2.0 and 1.2.1.
• In /administration/configuration/, remove the warning from:
  • retention-autocreate in the meta node's [meta] section
  • retention-autocreate in the data node's [meta] section
  • max-row-limit in the data node's [http] section

[timhallinflux]

Completed.