cleanup regarding to core StringUtils (openhab#15786)

Signed-off-by: Leo Siepel <[email protected]>

Author: lsiepel

bundles/org.openhab.binding.myq/src/main/java/org/openhab/binding/myq/internal/handler/MyQAccountHandler.java

@@ -29,7 +29,6 @@
 import java.util.Collection;
 import java.util.List;
 import java.util.Map;
-import java.util.Random;
 import java.util.Set;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ExecutionException;
@@ -621,17 +620,6 @@ private OAuthClientService getOAuthService() {
         return oAuthService;
     }
 
-    private static String randomString(int length) {
-        int low = 97; // a-z
-        int high = 122; // A-Z
-        StringBuilder sb = new StringBuilder(length);
-        Random random = new Random();
-        for (int i = 0; i < length; i++) {
-            sb.append((char) (low + (int) (random.nextFloat() * (high - low + 1))));
-        }
-        return sb.toString();
-    }
-
     private String generateCodeVerifier() {
         SecureRandom secureRandom = new SecureRandom();
         byte[] codeVerifier = new byte[32];