Revert "HTRACE-256 Change the artifactId for htrace-core in branch 4.0 to be htrace-core4; ADDENDUM"

This reverts commit eeda1121ee82776791d6ce7aca765a624fa85708.
diff --git a/pom.xml b/pom.xml
index 42e19ca..0e0342f 100644
--- a/pom.xml
+++ b/pom.xml
@@ -29,7 +29,7 @@
 
   <modules>
     <module>htrace-c</module>
-    <module>htrace-core4</module>
+    <module>htrace-core</module>
     <module>htrace-webapp</module>
     <module>htrace-zipkin</module>
     <module>htrace-hbase</module>