remove sidewall imp

1. for each bottom_thread(cc), 
2. - for each overlap_pair,
3. - - get median_a of each btm
4. - - get edges(a) from line_equation()
   
5. - - get valley-center(a) from edges(a)
6. - - get delta_r(center, median_a)
7. - - sidewall.append(bigger delta)
8. remove sidewalls and re-cc-analysis
9. for each bottom_thread(cc)
10. - for each non_overlap_pair,
11. - - #3-5
12. - - get delta_r(center, median_a) / width(a)
    
13. - - sidewall.append(delta > THRESH)
14. remove sidewalls and re-cc-analysis
15. update edge(3)