Move CacheHeaders to util.http and delete gwtexpui.server

This was the sole class remaining in the "server" package of gwtexpui;
we don't need a whole package for that.

Change-Id: I1df7d623e9823964b02903cef0d21334eb8cd9fc
diff --git a/plugins/BUILD b/plugins/BUILD
index 7252f8c..3852bc1 100644
--- a/plugins/BUILD
+++ b/plugins/BUILD
@@ -36,7 +36,7 @@
     "//java/com/google/gerrit/metrics",
     "//java/com/google/gerrit/metrics/dropwizard",
     "//java/com/google/gerrit/reviewdb:server",
-    "//java/com/google/gwtexpui/server",
+    "//java/com/google/gerrit/util/http",
     "//lib/commons:dbcp",
     "//lib/commons:lang",
     "//lib/commons:lang3",
@@ -110,7 +110,7 @@
         "//java/com/google/gerrit/server:libserver-src.jar",
         "//java/com/google/gerrit/server/restapi:librestapi-src.jar",
         "//java/com/google/gerrit/sshd:libsshd-src.jar",
-        "//java/com/google/gwtexpui/server:libserver-src.jar",
+        "//java/com/google/gerrit/util/http:libhttp-src.jar",
     ],
 )
 
@@ -125,8 +125,8 @@
         "//java/com/google/gerrit/common:annotations",
         "//java/com/google/gerrit/common:server",
         "//java/com/google/gerrit/extensions:api",
-        "//java/com/google/gwtexpui/server",
         "//java/com/google/gerrit/reviewdb:server",
+        "//java/com/google/gerrit/util/http",
     ],
     pkgs = ["com.google.gerrit"],
     title = "Gerrit Review Plugin API Documentation",