Delete theme/plugins directory

We have no custom plugins, so just toss this.
diff --git a/theme/plugins/README.md b/theme/plugins/README.md
deleted file mode 100644
index b3a4252..0000000
--- a/theme/plugins/README.md
+++ /dev/null
@@ -1 +0,0 @@
-placeholder
\ No newline at end of file