Remove deprecated theano.sandbox modules

theano/sandbox/blocksparse.py

-import warnings
-
-from theano.tensor.nnet.blocksparse import (
-    SparseBlockGemv,
-    SparseBlockOuter,
-    sparse_block_dot,
-    sparse_block_gemv,
-    sparse_block_gemv_inplace,
-    sparse_block_outer,
-    sparse_block_outer_inplace,
-)
-
-
-__all__ = [
-    SparseBlockGemv,
-    SparseBlockOuter,
-    sparse_block_dot,
-    sparse_block_gemv,
-    sparse_block_gemv_inplace,
-    sparse_block_outer,
-    sparse_block_outer_inplace,
-]
-
-warnings.warn(
-    "theano.sandbox.blocksparse does not exist anymore,"
-    "it has been moved to theano.tensor.nnet.blocksparse.",
-    category=DeprecationWarning,
-)

theano/sandbox/conv.py

-from warnings import warn
-
-
-warn(
-    "theano.sandbox.conv no longer provides conv. "
-    "They have been moved to theano.tensor.nnet.conv",
-    category=DeprecationWarning,
-)

theano/sandbox/softsign.py

-from theano.tensor.nnet.nnet import softsign  # noqa
-from warnings import warn
-
-
-warn(
-    "softsign was moved from theano.sandbox.softsign to theano.tensor.nnet.nnet ",
-    category=DeprecationWarning,
-)