Remove 6 hour limit



## Detailed Description
The blend service current ignores any forecast that are more than 6 hours old. We can remove this now as the blend weights are made dynamically

## Context
- new dynamic weights means we dont need hard cut off

## Possible Implementation
remove [this](https://github.com/openclimatefix/uk-pv-forecast-blend/blob/main/forecast_blend/utils.py#L10) function 
