Remove reference to branding plugin

JGit does not contribute to the Eclipse UI hence it should not refer
to a branding plugin. See discussion on egit-dev :
http://dev.eclipse.org/mhonarc/lists/egit-dev/msg00304.html until
http://dev.eclipse.org/mhonarc/lists/egit-dev/msg00306.html

Change-Id: I9153dea60d9d1724662ca079f16528a36c295b5d
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit-feature/feature.xml

@@ -3,8 +3,7 @@
       id="org.eclipse.jgit"
       label="%featureName"
       version="0.6.0.qualifier"
-      provider-name="%providerName"
+      provider-name="%providerName">
-      plugin="org.eclipse.egit">
 
    <description url="http://www.eclipse.org/egit/">
      %description