remove useless verification for non-null type

app/src/main/java/ovh/smayzy/i2d_project_15_app/MainActivity.kt

@@ -191,7 +191,7 @@ class MainActivity : AppCompatActivity() {
             xAxis.apply {
                 position = XAxis.XAxisPosition.BOTTOM
                 valueFormatter = object : ValueFormatter() {
-                    override fun getFormattedValue(value: Float): String? {
+                    override fun getFormattedValue(value: Float): String {
                         return "${value.toInt()}s"
                     }
                 }