Revert qiskit-community#400/qiskit-community#401 from stable branch

The change made in qiskit-community#400 (which was missed because it got integrated into
the qiskit-community#401 PR which was needed to unblock CI on master) should not have
been backported. It was only necessary for compat with terra master and
terra 0.15.0 because the validation module is removed in 0.15.0. This is
breaking measurement mitigation on the stable branch and 0.3.1 release
which needs to work with terra 0.14.x. This commit reverts that change
so the we're wrapping the counts in qiskit.validation.Obj and the
Results object is useable in marshmallow with released terra.

qiskit/ignis/mitigation/measurement/filters.py

@@ -24,6 +24,7 @@
 import scipy.linalg as la
 import numpy as np
 import qiskit
+from qiskit.validation.base import Obj
 from qiskit import QiskitError
 from qiskit.tools import parallel_map
 from ...verification.tomography import count_keys
@@ -150,7 +151,7 @@ def apply(self,
                 task_args=(raw_data, method))
 
             for resultidx, new_counts in new_counts_list:
-                new_result.results[resultidx].data.counts = new_counts
+                new_result.results[resultidx].data.counts = Obj(**new_counts)
 
             return new_result
 
@@ -329,7 +330,7 @@ def apply(self, raw_data, method='least_squares'):
                 task_args=(raw_data, method))
 
             for resultidx, new_counts in new_counts_list:
-                new_result.results[resultidx].data.counts = new_counts
+                new_result.results[resultidx].data.counts = Obj(**new_counts)
 
             return new_result