Deprecate three classes using HttpURLConnection.

Fixes #20323.

CHANGELOG.md

 # Changes in version 1.6.0 - 2016-??-??
 
+ * Major changes
+   - Deprecate DescriptorDownloader in favor of the much more widely
+     used DescriptorCollector.
+
  * Medium changes
    - Add two methods for loading and saving a parse history file in
      the descriptor reader to avoid situations where applications fail
@@ -17,6 +21,8 @@
      entries, and "(recommended|required)-(client|relay)-protocols"
      lines in consensuses and votes.
    - Parse "shared-rand-.*" lines in consensuses and votes.
+   - Deprecate DescriptorCollectorImpl now that
+     DescriptorIndexCollector is the default.
 
 
 # Changes in version 1.5.0 - 2016-10-19

src/main/java/org/torproject/descriptor/DescriptorDownloader.java

@@ -14,6 +14,9 @@ import java.util.Set;
  * setting any configuration options and initiating the download
  * process.</p>
  *
+ * @deprecated Removed as descriptor source in favor of the much more widely
+ *     used {@link DescriptorCollector}.
+ *
  * @since 1.0.0
  */
 public interface DescriptorDownloader {

src/main/java/org/torproject/descriptor/DescriptorRequest.java

@@ -15,6 +15,10 @@ import java.util.List;
  * {@link Descriptor} interface.  This container also stores potentially
  * useful meta-data about the descriptor request.</p>
  *
+ * @deprecated Removed as descriptor container together with
+ *     {@link DescriptorDownloader} in favor of the much more widely used
+ *     {@link DescriptorCollector}.
+ *
  * @since 1.0.0
  */
 public interface DescriptorRequest {

src/main/java/org/torproject/descriptor/impl/DescriptorCollectorImpl.java

@@ -32,6 +32,14 @@ import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 import java.util.zip.GZIPInputStream;
 
+/**
+ * Download files from a CollecTor instance based on the remote instance's
+ * directory listings.
+ *
+ * @deprecated Replaced by {@link DescriptorIndexCollector} which uses the
+ *     remote instance's index.json file as a more robust alternative to parsing
+ *     the remote instance's directory listings.
+ */
 public class DescriptorCollectorImpl implements DescriptorCollector {
 
   private static Logger log = LoggerFactory