Fix command_on_template for light_dimmer

[dchesterton]

The command_on_template should return a value between 0 and 99

[robertsLando]

@dchesterton Thanks! :)

[jshridha]

@robertsLando This actually reverts the code that was put in place by 771c68e. I agree that the brightness should return 0-99 for setting a new brightness. However, setting to 255 tells the light to turn on to the previous brightness that was set before the light was turned off. This is why 771c68e changed it from 99 to 255. I believe this commit should be reverted, but we can discuss if there's other opinions or if other lights act differently.