fix some minor inconsistencies in the naming of a few guc variables

the following guc variables have been renamed:

rdkit.ss_fp_size -> rdkit.sss_fp_size
rdkit.rdkit_difference_FP_weight_agents -> rdkit.difference_FP_weight_agents

references to rdkit.rdkit_difference_FP_weight_nonagents in the sql/expected files have been replaced with the actual name of the variable rdkit.difference_FP_weight_nonagents

NOTE: this changeset breaks the regression tests.