net-mgmt/netbox: Update to 2.10.3

• Prune obsolete update instructions/notes for NetBox releases prior 2.7.

Notable changes since 2.9.11:

It contains many bugfixes/enhancements and the following new features:

• Route Targets
• REST API bulk deletion
• REST API bulk update
• Reimplementation of custom fields
• Improved cable trace performance

https://github.com/netbox-community/netbox/blob/v2.10.3/docs/release-notes/version-2.10.md