Remove mender from documentation

[kprosise]

All mentions of mender have been removed or in the case of installing_mion.md, amended to add that it is now deprecated and linked to older documentation.

This applies to mion-docs #195

Signed-off-by: Katrina Prosise igorina@toganlabs.com

mion-docs

Summary

• Description: brief description of the bug that was fixed or the enhancement that was added
• Affected hardware: ALL -or- list specific switches
• Issue: #?

Build and test

• [x] Build command: mike deploy 2021.06-dev
• [x] Smoke tested on: http://localhost:8000/
• [x] all other steps taken to validate the pull request

Checklist

• [x] All relevant issues have been updated
• [x] Reviewers have been added and a maintainer has been assigned
• [x] A Label, Project and Milestone have all been added
• [x] The relevant documentation/wiki/README have been updated and complies with the NGL Style and Communication Guide
• [x] Git commits comply with the NGL Git Workflow and have DCO signoff
• [x] Yocto code complies with the OpenEmbedded Style Guide