Remove redundent function in Backtracking Sudoku (#4499)
Remove redundent function in Backtracking Sudoku (#4499)

* Remove redundent function

After reviewing this code, I've noticed that the `is_completed` function is a redundant operation.
Increasing the number of loops required for each step of the sudoku solver. 
This should remove n² operations where n is the width of the grid.

* Update sudoku.py

Remove additional newline
TheAlgorithms/Python