Change data-require to data-same-form

Changes adding_and_subtracting_rational_expressions_5
and adding_and_subtracting_rational_expressions_6 to
use data-same-form instead of data-simplify, because simplification
is hard and imperfect.

Test Plan:
Copy the answer from the hints of
localhost:8000/exercises/adding_and_subtracting_rational_expressions_5.html?debug&problem=0&seed=184
to the answer box, check that it works

Auditors: eater