Remove gif (Qiskit#13616)

* Remove gif

* Delete depth.gif

* Add explanatory snippet to depth method

* code review

Co-authored-by: Eric Arellano <[email protected]>

* Update quantumcircuit.py

---------

Co-authored-by: Eric Arellano <[email protected]>

Author: abbycross

docs/source_images/depth.gif

@@ -889,27 +889,6 @@ class QuantumCircuit:
 
        assert qc.size() == 19
 
-    A particularly important circuit property is known as the circuit :meth:`depth`.  The depth
-    of a quantum circuit is a measure of how many "layers" of quantum gates, executed in
-    parallel, it takes to complete the computation defined by the circuit.  Because quantum
-    gates take time to implement, the depth of a circuit roughly corresponds to the amount of
-    time it takes the quantum computer to execute the circuit.  Thus, the depth of a circuit
-    is one important quantity used to measure if a quantum circuit can be run on a device.
-
-    The depth of a quantum circuit has a mathematical definition as the longest path in a
-    directed acyclic graph (DAG).  However, such a definition is a bit hard to grasp, even for
-    experts.  Fortunately, the depth of a circuit can be easily understood by anyone familiar
-    with playing `Tetris <https://en.wikipedia.org/wiki/Tetris>`_.  Lets see how to compute this
-    graphically:
-
-    .. image:: /source_images/depth.gif
-       :alt: Rotate the circuit and let each gate fall as far as possible. The gates fall \
-              into "layers". The depth of the circuit is the number of layers.
-
-    We can verify our graphical result using :meth:`QuantumCircuit.depth`::
-
-       assert qc.depth() == 9
-
     .. automethod:: count_ops
     .. automethod:: depth
     .. automethod:: get_instructions
@@ -3490,6 +3469,14 @@ def depth(
     ) -> int:
         """Return circuit depth (i.e., length of critical path).
 
+        The depth of a quantum circuit is a measure of how many
+        "layers" of quantum gates, executed in parallel, it takes to
+        complete the computation defined by the circuit.  Because
+        quantum gates take time to implement, the depth of a circuit
+        roughly corresponds to the amount of time it takes the quantum
+        computer to execute the circuit.
+
+
         .. warning::
             This operation is not well defined if the circuit contains control-flow operations.