Removing legacy vuex module for monitoring connection

[nathanaelg16]

Summary

As part of my previous PR, connection monitoring has been moved away from using vuex state in favor of a composable that manages state globally. This PR removes the legacy vuex module that should no longer be in use.

References

• Creating composable for connection monitoring and replacing existing logic with it #12584
• Create composable for connection monitoring and replace existing logic with it #12205

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Testing checklist

• [X ] 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

• 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

[github-actions]

Build Artifacts

Asset type	Download link
PEX file	kolibri-0.17.0a0.dev0_git.107.g8196d62c.pex
Windows Installer (EXE)	kolibri-0.17.0a0.dev0+git.107.g8196d62c-windows-setup-unsigned.exe
Debian Package	kolibri_0.17.0a0.dev0+git.107.g8196d62c-0ubuntu1_all.deb
Mac Installer (DMG)	kolibri-0.17.0a0.dev0+git.107.g8196d62c.dmg
Android Package (APK)	kolibri-0.17.0a0.dev0+git.107.g8196d62c-0.1.4-debug.apk
TAR file	kolibri-0.17.0a0.dev0+git.107.g8196d62c.tar.gz
WHL file	kolibri-0.17.0a0.dev0+git.107.g8196d62c-py2.py3-none-any.whl

[rtibbles]

Changes look correct - manually tested and everything is fine. Manually ran linting, and no imports were undefined after this!