Remove navigation workaround for Vim mode

Upstream CodeMirror has fixed vim mode's problem of getting stuck in
hidden regions
(https://github.com/marijnh/CodeMirror/commit/6d1b5c4dafd60cc02eccf1d947e8c57e6afed8b9).
Removed mapping of "j", "k", "Up" and "Down".

Change-Id: I613a19ffa4126c42f5c46ee7b16841c95669b490
diff --git a/gerrit-gwtui/src/main/java/net/codemirror/lib/Loader.java b/gerrit-gwtui/src/main/java/net/codemirror/lib/Loader.java
index 2a515b7..46e7a71 100644
--- a/gerrit-gwtui/src/main/java/net/codemirror/lib/Loader.java
+++ b/gerrit-gwtui/src/main/java/net/codemirror/lib/Loader.java
@@ -94,10 +94,6 @@
       km.remove(s);
     }
     CodeMirror.addKeyMap("vim_ro", km);
-    CodeMirror.mapVimKey("j", "gj");
-    CodeMirror.mapVimKey("k", "gk");
-    CodeMirror.mapVimKey("Down", "gj");
-    CodeMirror.mapVimKey("Up", "gk");
   }
 
   private static void error(Exception e) {