Remove calculate-night-working-hours draft flow

Abigail Waraker said:
"We've reviewed this proposed smart answer and decided it's not worth going ahead with it as a tool but to put the information in flat content instead."
Replace ler variables with lel

The lel test is whether the person makes more than the lower earnings limit.
"ler" did not stand for anything meaningful
Merge pull request #1268 from alphagov/rename-lower-earnings-question

Replace ler variables with lel
Merge pull request #1267 from alphagov/remove-night-working-hours

Remove calculate-night-working-hours draft flow