Update Gauge.java

Author: Paultagoras

client-v2/src/main/java/com/clickhouse/client/api/internal/Gauge.java

@@ -18,9 +18,4 @@ public void set(long value) {
     public long getLong() {
         return value;
     }
-
-    @Override
-    public String getString() {
-        return String.valueOf(value);
-    }
 }