Remove the data directory.

Since the plugin_dir takes care of all plugins, there's no need to have
a data dir with a plugin dir for extinction anymore (for exodus, the
link was already gone).

diff --git a/data/extinction/plugin b/data/extinction/plugin
deleted file mode 120000 (symlink)
index 5622cf3..0000000
--- a/data/extinction/plugin
+++ /dev/null
@@ -1 +0,0 @@
-../../plugin
\ No newline at end of file