Buck: Remove jgit cell

Cross cell support in Buck is considered as experimental feature, with
number of open issues: [1], [2], [3].  Moreover, to make Maven Central
machinery work, it was needed to create symbolic links in source tree.
That broke `buck targets` feature.

Remove it for now, and re-consider to add it later.

[1] https://github.com/facebook/buck/issues/656
[2] https://github.com/facebook/buck/issues/658
[3] https://github.com/facebook/buck/issues/717

Bug: Issue 3954
Change-Id: Ic621a07771f926001df181b46b2169e214ce208a

gerrit-util-http/BUCK

@@ -15,7 +15,7 @@ java_library(
     '//lib:guava',
     '//lib:servlet-api-3_1',
     '//lib/httpcomponents:httpclient',
-    '@jgit//org.eclipse.jgit:jgit',
+    '//lib/jgit/org.eclipse.jgit:jgit',
   ],
   visibility = ['PUBLIC'],
 )