revert stable-crust gridded b-value
Revert stable-crust gridded b-values back to 1.0 (the same value used in 2018 model) from the decluster-method-specific b-values.
Confirmed that rate values in stable-crust/grid/*/*/*/rate-tree.json
files match the annualized 10^ai (from gridding) values in Nb_values_v3.xlsx
See #25 (closed)