Updating docs to remove retired machines (Comet@SDSC, Cooley@ALCF, Theta@ALCF) (#3095)

Author: yadudoc

docs/userguide/configuring.rst

@@ -531,17 +531,6 @@ Center's **Expanse** supercomputer. The example is designed to be executed on th
 .. literalinclude:: ../../parsl/configs/expanse.py
 
 
-Cooley (ALCF)
--------------
-
-The following snippet shows an example configuration for executing on Argonne Leadership Computing Facility's
-**Cooley** analysis and visualization system.
-The example uses the `parsl.executors.HighThroughputExecutor` and connects to Cooley's Cobalt scheduler
-using the `parsl.providers.CobaltProvider`. This configuration assumes that the script is being executed on the login nodes of Theta.
-
-.. literalinclude:: ../../parsl/configs/cooley.py
-
-
 .. _configuring_nersc_cori:
 
 Perlmutter (NERSC)
@@ -628,18 +617,6 @@ The example uses the `parsl.providers.LSFProvider` to provision compute nodes fr
 .. literalinclude:: ../../parsl/configs/summit.py
 
 
-Theta (ALCF)
-------------
-
-.. image:: https://www.alcf.anl.gov/files/ALCF-Theta_111016-1000px.jpg
-
-The following snippet shows an example configuration for executing on Argonne Leadership Computing Facility's
-**Theta** supercomputer. This example uses the `parsl.executors.HighThroughputExecutor` and connects to Theta's Cobalt scheduler
-using the `parsl.providers.CobaltProvider`. This configuration assumes that the script is being executed on the login nodes of Theta.
-
-.. literalinclude:: ../../parsl/configs/theta.py
-
-
 TOSS3 (LLNL)
 ------------