* Update Light flash description
`light.turn_on` service description for the `flash` option gave the impression of a boolean value being required when in fact a string of either `short` or `long` was required. Updated this to match the documentation found at https://www.home-assistant.io/integrations/light
`light.turn_off` also described the existence of a `flash` option when none exists. I've removed this, which matches the aforementioned documentation too.
* Revert removal of flash from turn-off
As discussed in feedback, turn-off does indeed seem to support flash.
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