lint: fix pyflakes errors

To reproduce the errors:
```
ruff check --select "F" black_it tests examples scripts
```

This will first give the following error:
```
examples/models/economics/brock_hommes.py:62:5: F841 [*] Local variable `pStar` is assigned to but never used
```

once fixed, running the same command again will give the following error:

```
examples/models/economics/brock_hommes.py:54:5: F841 [*] Local variable `div` is assigned to but never used
```

Once fixed the last error, pyflakes does not detect any other issue.

examples/models/economics/brock_hommes.py

@@ -51,15 +51,13 @@ def BH2(theta: Sequence[float], N: int, seed: int):
     beta = 3.6
     sigma = 1.0
     a = 1.0
-    div = 0.1
     divEpsMin = 0  # -0.05
     divEpsMax = 0  # 0.05
     C = 1.0
 
     x_lag2 = 0.10
     x_lag1 = 0.10
 
-    pStar = div / (R - 1)
     bsa = beta / (a * (sigma**2))
 
     x = np.zeros(N + 2)