FilteredRefDatabase: Remove getRef(String name) override

The latest JGit release marked getRef() final, so that it cannot be
overridden any more. It's not relevant anyway, because exactRef() does
the job and it is overridden and takes permissions into consideration.

Change-Id: I4f9015a41105a3c893970cf026d87007315ce01d

src/main/java/com/googlesource/gerrit/plugins/gitiles/FilteredRepository.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/gitiles/FilteredRepository.java b/src/main/java/com/googlesource/gerrit/plugins/gitiles/FilteredRepository.java
index 0a4d3bf..e0c7928 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/gitiles/FilteredRepository.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/gitiles/FilteredRepository.java
@@ -206,20 +206,6 @@
     }
 
     @Override
-    public Ref getRef(String name) throws IOException {
-      Ref ref = git.getRefDatabase().getRef(name);
-      if (ref == null) {
-        return null;
-      }
-      try {
-        return perm.filter(ImmutableMap.of(ref.getName(), ref), git, RefFilterOptions.defaults())
-            .get(ref.getName());
-      } catch (PermissionBackendException e) {
-        throw new IOException(e);
-      }
-    }
-
-    @Override
     public Map<String, Ref> getRefs(String prefix) throws IOException {
       Map<String, Ref> refs;
       try {