Revert "Add 1.9.2 back in"

This reverts commit c782bbc666b37b714822f07c221b139d19dbe918.

BigDecimal on 1.9.2, meh.
It's the EFG scheme nowadays.
Convert Phase to a static association model.
Use phase-specific euro conversation rate.
Move euro_conversion_rate from PremiumSchedule to Loan.

The value is taken from the newest type S premium schedule for a loan, when one isn't available (it's supposed to be but unfortunately this isn't always the case) it's pulled from the first premium schedule.
Initial work on Phase 6 calculator
Update loan entry to support Phase 6 state aid calculation
We just need an eligible loan at this point.
Use a standard validation.
Use a central rules object rather than scattering logic across the app.
A phase 6 type E loan has a maximum term of 3 years.
Ensure phase 6 amount/term constraints are applied in loan changes.
Fetch correct validation message.
Convert eligibility check to a Validator.
Unused.
Use existing RepaymentDurationValidator in the eligibility check.
Change error message for repayment duration validator
Don't redirect to state aid field in loan entry form
Phase 5 and 6 specific eligibility and loan entry validations
Generate premium schedule now opens creation form
if a loan does not have a premium schedule