Remove unused truedot.py module with unnecessary tests imports

setup.cfg

 [flake8]
 ignore=E501,E123,E133,FI12,FI14,FI15,FI50,FI51,FI53,W503,W504,E203,C901,E231,E741
 per-file-ignores =
-    theano/sparse/sandbox/truedot.py:F401
     theano/sparse/sandbox/sp2.py:F401
     tests/sparse/test_basic.py:E402
     tests/sparse/test_opt.py:E402

theano/sparse/sandbox/truedot.py

-import theano
-import numpy as np
-import scipy.sparse as sp
-
-from theano import sparse
-from theano import gof, tensor, compile
-
-from theano.sparse.basic import (
-    _is_sparse_variable,
-    _is_dense_variable,
-    as_sparse_variable,
-    _is_sparse,
-    _mtypes,
-    _mtype_to_str,
-)
-from theano.sparse import SparseType, dense_from_sparse, transpose
-
-from tests import unittest_tools as utt
-from tests.sparse.test_basic import eval_outputs
-from tests.theano.sparse.test_basic import sparse_random_inputs
-
-# To maintain compatibility
-from theano.sparse.basic import TrueDot, true_dot