remove pytensor/sandbox/solve.py as it is marked deprecated

pytensor/sandbox/solve.py

-import warnings
-
-
-from pytensor.tensor.slinalg import solve  # noqa
-
-message = (
-    "The module pytensor.sandbox.solve will soon be deprecated.\n"
-    "Please use tensor.slinalg.solve instead."
-)
-
-warnings.warn(message)