drop obsolete import (#177)

Author: davidkarlsen

simpleclient_hotspot/src/test/java/io/prometheus/client/hotspot/StandardExportsTest.java

@@ -8,7 +8,6 @@
 import java.io.BufferedReader;
 import java.io.StringReader;
 import java.io.FileNotFoundException;
-import java.util.Vector;
 import java.lang.management.RuntimeMXBean;
 
 import io.prometheus.client.CollectorRegistry;