Update test_select_time_slice.py

# Pull Request

## Description

This PR removes `max_steps_gap` and `fill_selection` parameters and `_sel_fillinterp()` and `_sel_fillnan()` as they are no longer required for training.

Fixes openclimatefix#107

## Checklist:

- [.] My code follows [OCF's coding style guidelines](https://github.com/openclimatefix/.github/blob/main/coding_style.md)
- [.] I have performed a self-review of my own code
- [ ] I have made corresponding changes to the documentation
- [ ] I have added tests that prove my fix is effective or that my feature works
- [.] I have checked my code and corrected any misspellings

tests/select/test_select_time_slice.py

@@ -99,7 +99,6 @@ def test_select_time_slice_out_of_bounds(da_sat_like, t0_str):
         interval_start=interval_start,
         interval_end=interval_end,
         sample_period_duration=freq,
-        fill_selection=True
     )
 
     # Check the returned times are as expected