Remove old langchain test suites from ignore list (#4737)

Forgot to remove these two from the toxgen ignore list. Shouldn't have
any actual effect on tests since the test suites are now called
differently.

Author: sentrivana

scripts/populate_tox/populate_tox.py

@@ -74,8 +74,6 @@
     "chalice",
     "gcp",
     "httpx",
-    "langchain",
-    "langchain_notiktoken",
     "pure_eval",
     "quart",
     "ray",