Remove warning from AC dimmer component (#5759)

The referenced feature request has not been commented on in over 5 years, and hasn't been mentioned in almost 4 years. It seems like this warning isn't relevant anymore.

Author: pzich

content/components/output/ac_dimmer.md

@@ -7,13 +7,6 @@ params:
     image: ac_dimmer.svg
 ---
 
-> [!WARNING]
-> This component has not been fully tested yet, if you are testing this component
-> please share your experience with the dimmer hardware and light model and
-> configuration here <https://github.com/esphome/feature-requests/issues/278>
->
-> Thanks!
-
 The `ac_dimmer` component allows you to connect a dimmable light or other load
 which supports phase control dimming to your ESPHome project.