fix 3 javac warnings: redundant cast

see GitHub issue #561 for context

    [javac] /home/thk/git/yacy_search_server/source/net/yacy/htroot/ConfigAccounts_p.java:85: warning: [cast] redundant cast to YaCyHttpServer
    [javac]                 final YaCyHttpServer jhttpserver = (YaCyHttpServer)sb.getHttpServer();
    [javac]                                                    ^
    [javac] /home/thk/git/yacy_search_server/source/net/yacy/htroot/ConfigUser_p.java:156: warning: [cast] redundant cast to YaCyHttpServer
    [javac]                 final YaCyHttpServer jhttpserver = (YaCyHttpServer) sb.getHttpServer();
    [javac]                                                    ^
    [javac] /home/thk/git/yacy_search_server/source/net/yacy/htroot/ConfigUser_p.java:167: warning: [cast] redundant cast to YaCyHttpServer
    [javac]             final YaCyHttpServer jhttpserver = (YaCyHttpServer) sb.getHttpServer();

source/net/yacy/htroot/ConfigAccounts_p.java

@@ -82,7 +82,7 @@ public class ConfigAccounts_p {
                 env.setConfig(SwitchboardConstants.ADMIN_ACCOUNT_B64MD5,  sb.encodeDigestAuth(user, pw1));
                 env.setConfig(SwitchboardConstants.ADMIN_ACCOUNT_USER_NAME,user);
                 // make sure server accepts new credentials
-                final YaCyHttpServer jhttpserver = (YaCyHttpServer)sb.getHttpServer();
+                final YaCyHttpServer jhttpserver = sb.getHttpServer();
                 if (!user.equals(oldusername)) jhttpserver.removeUser(oldusername);
                 jhttpserver.resetUser(user);
             } else {

source/net/yacy/htroot/ConfigUser_p.java

@@ -153,7 +153,7 @@ public class ConfigUser_p {
                 } catch (final Exception e) {
                     ConcurrentLog.logException(e);
                 }
-                final YaCyHttpServer jhttpserver = (YaCyHttpServer) sb.getHttpServer();
+                final YaCyHttpServer jhttpserver = sb.getHttpServer();
                 jhttpserver.resetUser(entry.getUserName());
             } else {
                 prop.put("error", "1");
@@ -164,7 +164,7 @@ public class ConfigUser_p {
             prop.putHTML("username", username);
         } else if (post.containsKey("delete")) {
             sb.userDB.removeEntry(post.get("username"));
-            final YaCyHttpServer jhttpserver = (YaCyHttpServer) sb.getHttpServer();
+            final YaCyHttpServer jhttpserver = sb.getHttpServer();
             jhttpserver.removeUser(post.get("username"));
             prop.put(serverObjects.ACTION_LOCATION, "ConfigAccountList_p.html"); // jump back to user list
         }