Changes

Removing l_interp_prescribed_params from setup_clubb_pdf_params.
The flag has been removed and so has any code underneat a logic statement
involving this statement unless it has multiple flags. The else statement
in the if block involving this flag has been set to execute without an
if block.
For ticket #916
Results are BFB identical. Additionally, complex logic statements
with the use of more flags had those flags adjusted and BFB results
were also confirmed with these changes.