Revert D32599540: [pytorch][PR] implemented 'torch.distributions.constraints.symmetric' checking if the tensor is symmetric at last 2 dimension.

Test Plan: revert-hammer

Differential Revision:
D32599540 (https://github.com/pytorch/pytorch/commit/bc3bdbc8f48ff42238feb949fd7812b0a20bc329)

Original commit changeset: 9227f7e99318

fbshipit-source-id: edfe7072073d910a49be52e1b8c2d374ef71e9ec
diff --git a/test/distributions/test_constraints.py b/test/distributions/test_constraints.py
index f1fc35a..6c6e392 100644
--- a/test/distributions/test_constraints.py
+++ b/test/distributions/test_constraints.py
@@ -7,13 +7,6 @@
 from torch.testing._internal.common_cuda import TEST_CUDA
 
 
-EXAMPLES = [
-    (constraints.symmetric, False, [[2., 0], [2., 2]]),
-    (constraints.positive_definite, True, [[2., 0], [2., 2]]),
-    (constraints.symmetric, True, [[3., -5], [-5., 3]]),
-    (constraints.positive_definite, False, [[3., -5], [-5., 3]]),
-]
-
 CONSTRAINTS = [
     (constraints.real,),
     (constraints.real_vector,),
@@ -48,15 +41,6 @@
     t = torch.cuda.DoubleTensor if is_cuda else torch.DoubleTensor
     return constraint_fn(*(t(x) if isinstance(x, list) else x for x in args))
 
-@pytest.mark.parametrize('constraint_fn, result, value', EXAMPLES)
-@pytest.mark.parametrize('is_cuda', [False,
-                                     pytest.param(True, marks=pytest.mark.skipif(not TEST_CUDA,
-                                                                                 reason='CUDA not found.'))])
-def test_constraint(constraint_fn, result, value, is_cuda):
-    t = torch.cuda.DoubleTensor if is_cuda else torch.DoubleTensor
-    assert constraint_fn.check(t(value)).all() == result, \
-        "Error in checking postive example of {}".format(constraint_fn)
-
 
 @pytest.mark.parametrize('constraint_fn, args', [(c[0], c[1:]) for c in CONSTRAINTS])
 @pytest.mark.parametrize('is_cuda', [False,
diff --git a/torch/distributions/constraints.py b/torch/distributions/constraints.py
index 3acf04a..5eed19a 100644
--- a/torch/distributions/constraints.py
+++ b/torch/distributions/constraints.py
@@ -22,7 +22,6 @@
 - ``constraints.real_vector``
 - ``constraints.real``
 - ``constraints.simplex``
-- ``constraints.symmetric``
 - ``constraints.stack``
 - ``constraints.unit_interval``
 """
@@ -55,7 +54,6 @@
     'real_vector',
     'simplex',
     'stack',
-    'symmetric',
     'unit_interval',
 ]
 
@@ -458,16 +456,6 @@
         return _LowerCholesky().check(value) & unit_row_norm
 
 
-class _Symmetric(Constraint):
-    """
-    Constrain to Symmetric square matrices.
-    """
-    event_dim = 2
-
-    def check(self, value):
-        return (value.transpose(-2, -1) == value).all(dim=-1).all(dim=-1)
-
-
 class _PositiveDefinite(Constraint):
     """
     Constrain to positive-definite matrices.
@@ -569,7 +557,6 @@
 lower_triangular = _LowerTriangular()
 lower_cholesky = _LowerCholesky()
 corr_cholesky = _CorrCholesky()
-symmetric = _Symmetric()
 positive_definite = _PositiveDefinite()
 cat = _Cat
 stack = _Stack