Originally these tests verified that at a SelectCoins level that a
solution with fewer inputs gets preferred at high feerates, and a
solution with more inputs gets preferred at low feerates. This outcome
relies on the behavior of BnB, so we move these tests under the umbrella
of BnB tests.
Originally these tests relied on SFFO to work.
Recreates the tests in a new test suite coinselection_tests.cpp that is
based on UTXOs being created per their effective values rather than
nominal values and uses transactions with non-zero feerates.
