tests: test pip install plugin with no-dependency package

This is a simplification to help ensure we don't run into issues like
below because requests gets installed via pip.

```
RemoveError: 'requests' is a dependency of conda and cannot be removed from conda's operating environment.
```

integration-tests/plugins/simplest/tljh_simplest.py

@@ -12,7 +12,7 @@ def tljh_extra_user_conda_packages():
 
 @hookimpl
 def tljh_extra_user_pip_packages():
-    return ["django"]
+    return ["simplejson"]
 
 
 @hookimpl

integration-tests/test_simplest_plugin.py

@@ -20,7 +20,7 @@ def test_tljh_extra_user_conda_packages():
 
 
 def test_tljh_extra_user_pip_packages():
-    subprocess.check_call([f"{USER_ENV_PREFIX}/bin/python3", "-c", "import django"])
+    subprocess.check_call([f"{USER_ENV_PREFIX}/bin/python3", "-c", "import simplejson"])
 
 
 def test_tljh_extra_hub_pip_packages():