Update git submodules

* Update docs/submodules/appc.git from branch 'master'
  to a6fbd20042f03a46084c2b068c21d1a691a7d836
  - Remove duplicate versions
    
    These versions are inherited from opendaylight parent
    poms. Removing the override for these inherited versions.
    
    Change-Id: I83b374e4d8815e21fd48bedbe4dd46bc246e44a4
    Signed-off-by: Patrick Brady <patrick.brady@att.com>
    Issue-ID: APPC-1355
    
diff --git a/docs/submodules/appc.git b/docs/submodules/appc.git
index 1a285b3..a6fbd20 160000
--- a/docs/submodules/appc.git
+++ b/docs/submodules/appc.git
@@ -1 +1 @@
-Subproject commit 1a285b3b92e3253c9e1ae45c42be1c157f5120e9
+Subproject commit a6fbd20042f03a46084c2b068c21d1a691a7d836