arm-22: Fix anova_radon_nopred.stan, generate Fig. 22.4

- anova_radon_nopred.stan didn't compile due to duplicate vars in "generated quantities" block
- Generate something close to Figure 22.4
Merge pull request #669 from casallas/feature/ARM-patch22.4

ARM, Chapter 22: Fix anova_radon_nopred.stan, generate Figure 22.4