refactor: rm direct dp.emit() call in constructor.

[Mrpaoo]

What does this PR do?
Remove the dp.emit() call in constructor, at this time, the dp isn't connect to callback, so it make no sense.

Related issues
N/A

Checklist

• Code is formatted with clang-format
• Builds locally (ninja -C build)
• Man page updated for any new/changed user-facing option (man/)
• Tested against the affected module(s)

[Mrpaoo]

However, dp.emit() still call before the dp.connect according to the #5200 (comment), which thread could call dp.emit() before connected. I would track this down in #5205