Remove wohnort_ost from simple_example notebook. (#1087)

### What problem do you want to solve?

@felixschmitz made me aware that we have `wohnort_ost` as an input
there. This PR removes it.

- The input is not necessary at all in 2025.
- It leads to errors in the years before because the actual input name
should be `wohnort_ost_hh`.

Author: MImmesberger

docs/tutorials/simple_example.ipynb

@@ -140,7 +140,6 @@
     "        \"birth_year\": [1995, 1995, 2015],\n",
     "        \"hh_id\": [0, 0, 0],\n",
     "        \"p_id\": [0, 1, 2],\n",
-    "        \"east_germany\": [False, False, False],\n",
     "        \"self_employed\": [False, False, False],\n",
     "        \"income_from_self_employment\": [0, 0, 0],\n",
     "        \"income_from_rent\": [0, 0, 0],\n",
@@ -191,7 +190,6 @@
     "    \"geburtsjahr\": \"birth_year\",\n",
     "    \"hh_id\": \"hh_id\",\n",
     "    \"p_id\": \"p_id\",\n",
-    "    \"wohnort_ost\": \"east_germany\",\n",
     "    \"einnahmen\": {\n",
     "        \"bruttolohn_m\": \"income_from_employment\",\n",
     "        \"kapitalerträge_m\": \"income_from_capital\",\n",