Fix redundant system event

[mthenw]

What did you implement:

It fixes publishing the same system event twice for sync subscriptions.

Todos:

• Write tests
• Write documentation
• Fix linting errors
• Make sure code coverage hasn't dropped
• Provide verification commands / resources
• Enable "Allow edits from maintainers" for this PR
• Update the messages below

Is this ready for review?: Yes
Is it a breaking change?: No

[codecov]

Codecov Report

Merging #489 into master will increase coverage by 0.13%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #489      +/-   ##
==========================================
+ Coverage   70.84%   70.97%   +0.13%     
==========================================
  Files          37       37              
  Lines        2195     2188       -7     
==========================================
- Hits         1555     1553       -2     
+ Misses        576      572       -4     
+ Partials       64       63       -1

Impacted Files	Coverage Δ
router/router.go	64.91% <100%> (+0.81%)	⬆️

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