ARKODE Stepper SetDefaults memory leak fix

[drreynolds]

Updated stepper SetDefaults routines to deallocate pre-existing structures before nullifying, and moved initial creation of the SUNAdaptController into stepper SetDefaults routines instead of arkCreate. This allows non-adaptive steppers to leave the SUNAdaptController object unallocated.

[gardner48]

Other than the minor suggestion to remove an erroneous new line, do arkPrintAdaptMem and arkAdapt also need checks for a NULL controller?

[drreynolds]

Other than the minor suggestion to remove an erroneous new line, do arkPrintAdaptMem and arkAdapt also need checks for a NULL controller?

The NULL check was indeed necessary in arkPrintAdaptMem. I added it to arkAdapt as well just in case, but since any non-adaptive stepper (who leaves a NULL-valued SUNAdaptController) must also set ark_mem->fixedstep to SUNTRUE, that check should be redundant.