Revert "refactor: move test-plugin to integration suite"

This reverts commit bc02005dc0.

I couldn't get past some GLIBC errors in CI so moving back to unit
tests.

test/tsconfig.json

@@ -1,4 +1,5 @@
 {
   "extends": "../tsconfig.json",
-  "include": ["./**/*.ts"]
+  "include": ["./**/*.ts"],
+  "exclude": ["./unit/node/test-plugin"]
 }