Perform fewer workarounds for scalar blocks
Perform fewer workarounds for scalar blocks

The option to natively compute a and b derivatives has been around for
awhile. If we just force the user to supply this option, we can trim the
code by quite a bit.

Signed-off-by: Connor Behan <89f96a099c47edae2e9c5a371cbf43991ac7aa8c@gmail.com>

cbehan/pycftboot