Remove unused import assertThrows from StochasticMatrixTest

Removed unused import for assertThrows.

Author: Dsannue

src/test/java/com/thealgorithms/matrix/StochasticMatrixTest.java

@@ -1,7 +1,6 @@
 package com.thealgorithms.matrix;
 
 import static org.junit.jupiter.api.Assertions.assertFalse;
-import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import org.junit.jupiter.api.Test;