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

lib/jgit/org.eclipse.jgit.junit/BUCK

@@ -8,5 +8,5 @@ maven_jar(
   license = 'DO_NOT_DISTRIBUTE',
   repository = REPO,
   unsign = True,
-  deps = ['@jgit//org.eclipse.jgit:jgit'],
+  deps = ['//lib/jgit/org.eclipse.jgit:jgit'],
 )