Add missing stacklevel param from dagcircuit DeprecationWarnings (#4230)
Add missing stacklevel param from dagcircuit DeprecationWarnings (#4230)

There were several places deprecation warnings are emitted in the
DAGCircuit class. However, none of these deprecations set a stacklevel
kwarg which means the default of 1 is used. This means the deprecation
warnings refer to the warn() line as the source of the deprecation
instead of the caller of the function. This commit corrects this
oversight by adding stacklevel=2 which will show the caller as the
source of the deprecation warning.
QISKit/qiskit-sdk-py,QISKit/qiskit-sdk-py,QISKit/qiskit-sdk-py