removed pleineLune from submodules

.gitmodules

-[submodule "plugins/PleineLune"]
-    path = plugins/PleineLune
-    url = https://github.com/piwik/theme-PleineLune.git
-    branch = master
 [submodule "plugins/SecurityInfo"]
     path = plugins/SecurityInfo
     url = https://github.com/piwik/plugin-SecurityInfo.git
@@ -42,4 +38,4 @@
 [submodule "libs/PiwikTracker"]
     path = libs/PiwikTracker
     url = https://github.com/piwik/piwik-php-tracker.git
-    branch = master
\ No newline at end of file
+    branch = master