Remove terminally deprecated constructor in java.net.URLDecoder

Summary

The constructor of java.net.URLDecoder was terminally deprecated and should be removed.

Problem

Default constructor accidentally included in a class.

Solution

Remove the terminally deprecated constructor by making it private.

Specification

--- a/src/java.base/share/classes/java/net/URLDecoder.java
+++ b/src/java.base/share/classes/java/net/URLDecoder.java
@@ -84,8 +84,7 @@ public class URLDecoder {
     /**
      * Do not call.
      */
-    @Deprecated(since="16", forRemoval=true)
-    public URLDecoder() {}
+    private URLDecoder() {}

     // The platform default encoding
     static String dfltEncName = URLEncoder.dfltEncName;