Remove importing PauliSumOp, which is deprecated. (#1079)

---------

Co-authored-by: Jake Lishman <jake.lishman@ibm.com>
Co-authored-by: Kevin Tian <kevin.tian@ibm.com>

qiskit_ibm_runtime/estimator.py

@@ -16,9 +16,9 @@
 import os
 from typing import Optional, Dict, Sequence, Any, Union
 import logging
+import typing
 
 from qiskit.circuit import QuantumCircuit
-from qiskit.opflow import PauliSumOp
 from qiskit.quantum_info.operators.base_operator import BaseOperator
 from qiskit.primitives import BaseEstimator
 
@@ -32,6 +32,9 @@
 # pylint: disable=unused-import,cyclic-import
 from .session import Session
 
+if typing.TYPE_CHECKING:
+    from qiskit.opflow import PauliSumOp
+
 logger = logging.getLogger(__name__)