Remove hint and concept documentation references

Removed documentation references for hints and concepts.

Author: zonedoutdg

Problems/Mathematics/Day-03/q002.md

@@ -71,5 +71,3 @@ In the second sample one can connect two resistors in parallel (obtaining resist
 ---
 [PROBLEM LINK](https://codeforces.com/contest/343/problem/A)
 
-refer to the documentation below for hints and concept:
-[ref:](https://en.wikipedia.org/wiki/Calkin%E2%80%93Wilf_tree)