LDV: add charging_efficiency condition

# :rocket:

- [ x] Is your feature request essential for your project?

### Describe the workflow you want to enable

We would like have charging efficiency vary according to the power parameter input

### Describe your proposed implementation, if applicable

1. Add the following condition:
```
if power > 19.2, charging efficiency=0.95
else charging_efficiency = 0.9
```
2. Make `charging_efficiency` a parameter in relevant functions instead using the value from `const.py`
3. Remove charging efficiency and ER values from `const.py`

Example in existing code can be found here:
https://github.com/isond/PreREISE/blob/fc6ed851fc9fbdc0a65b309ab37aa51bbfe8a84c/prereise/gather/demanddata/transportation_electrification/smart_charging_HDV.py#L261

### Additional context
Add any other context or screenshots in this section, e.g., a plot from an article you
believe would clearly communicate results.