Remove telescope-specific rotation code in pixel plotting

Currently in ```plot_pixels.py``` we are applying telescope-specific rotation by hardcoding it using if/else statements like follows:

```
    if "SST" in array_element_type or "SCT" in array_element_type:
        total_rotation = (90 * u.deg) - rotate_angle
    else:
        total_rotation = (-90 * u.deg) - rotate_angle
```