This was introduced by some changes to shinyapp.js that were necessary
before async outputs and sync outputs were held/flushed together. Now
that async/sync outputs are held/flushed together, these changes are
not necessary and removing them fixes the problem.
The test app is in shiny-examples/205-async-req. I also moved a test
app from manualtests/async/download.R to shiny-examples/204-async-download.
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