[Fix] Remove scipy.misc (#669)

With the latest scipy 1.15 release `scipy.misc` was deprecated which
triggers a warning in autograd:
```
DeprecationWarning: scipy.misc is deprecated and will be removed in 2.0.0
    import scipy.misc as osp_misc
```

We only use the misc module to provide `logsumexp` which has been moved
to `scipy.special` many years ago, so removing the functionality should
not change anything for users on python>=3.9.

I also changed the import in the fluidsim example
([imread](https://docs.scipy.org/doc/scipy-1.2.3/reference/generated/scipy.ndimage.imread.html#scipy.ndimage.imread)
is deprecated in SciPy 1.0.0. Use matplotlib.pyplot.imread instead)

autograd/scipy/__init__.py

@@ -1,6 +1 @@
 from . import integrate, signal, special, stats
-
-try:
-    from . import misc
-except ImportError:
-    pass

examples/fluidsim/fluidsim.py

@@ -2,7 +2,7 @@
 
 import matplotlib
 import matplotlib.pyplot as plt
-from scipy.misc import imread
+from matplotlib.pyplot import imread
 from scipy.optimize import minimize
 
 import autograd.numpy as np