Removing pip plugin since it was not used.

```
% devbox add pip

Error: Package pip not found
```

we also moved `venvShellHook.sh` to a python directory.

Author: djgoku

plugins/pip.json

@@ -6,7 +6,7 @@
     "VENV_DIR": "{{ .DevboxProjectDir }}/.venv"
   },
   "create_files": {
-    "{{ .Virtenv }}/bin/venvShellHook.sh": "pip/venvShellHook.sh"
+    "{{ .Virtenv }}/bin/venvShellHook.sh": "python/venvShellHook.sh"
   },
   "shell": {
     "init_hook": ["{{ .Virtenv }}/bin/venvShellHook.sh"]