Prevent learner only devices from being shown as an import source when creating one.

[rtibbles]

Summary

Prevents us from showing subset of user devices when importing learner(s) to create a subset of user device

References

Fixes #11749

Reviewer guidance

Startup an already provisioned learner only device
Startup a fresh Kolibri env with this fix
Go through the learner only device flow
See that the already provisioned learner only device does not show up in the device selection modal

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Testing checklist

• Contributor has fully tested the PR manually
• If there are any front-end changes, before/after screenshots are included
• Critical user journeys are covered by Gherkin stories
• Critical and brittle code paths are covered by unit tests

PR process

• PR has the correct target branch and milestone
• PR has 'needs review' or 'work-in-progress' label
• If PR is ready for review, a reviewer has been added. (Don't use 'Assignees')
• If this is an important user-facing change, PR or related issue has a 'changelog' label
• If this includes an internal dependency change, a link to the diff is provided

Reviewer checklist

• Automated test coverage is satisfactory
• PR is fully functional
• PR has been tested for accessibility regressions
• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
• Contributor is in AUTHORS.md

[nucleogenesis]

Code LGTM

[rtibbles]

Will wait on manual QA to merge.

[github-actions]

Build Artifacts

Asset type	Download link
PEX file	kolibri-0.16.0b10.dev0_git.175.g842d5e09.pex
Windows Installer (EXE)	kolibri-0.16.0b10.dev0+git.175.g842d5e09-unsigned.exe
Debian Package	kolibri_0.16.0b10.dev0+git.175.g842d5e09-0ubuntu1_all.deb
Mac Installer (DMG)	kolibri-0.16.0b10.dev0+git.175.g842d5e09-0.3.0.dmg
Android Package (APK)	kolibri-0.16.0b10.dev0+git.175.g842d5e09-0.1.0-debug.apk
TAR file	kolibri-0.16.0b10.dev0+git.175.g842d5e09.tar.gz
WHL file	kolibri-0.16.0b10.dev0+git.175.g842d5e09-py2.py3-none-any.whl

[radinamatic]

Other LoDs and confusing strings are no more! 💥

[radinamatic]

Manual QA passes, good to go! 💯