Keep only ES using Heat Equation

Not much is gained by keeping these around,
and there's less to maintain.

notebooks/ES_2D_Heat_Equation.py

@@ -6,7 +6,7 @@
 #       extension: .py
 #       format_name: percent
 #       format_version: '1.3'
-#       jupytext_version: 1.14.5
+#       jupytext_version: 1.16.0
 #   kernelspec:
 #     display_name: Python 3 (ipykernel)
 #     language: python
@@ -37,8 +37,6 @@
 
 from p_tqdm import p_map
 
-import iterative_ensemble_smoother as ies
-
 # %%
 # %load_ext autoreload
 # %autoreload 2
@@ -487,22 +485,6 @@ def plot_responses(
 # Setting negative values to a small positive value but not zero because we want to be able to divide by them.
 A_ES = A_ES.clip(min=1e-8)
 
-# %% [markdown]
-# ## Testing the new iterative_ensemble_smoother package
-#
-# As part of ERT development, we wrote an efficient implementation of the iterative ensemble smoother.
-# This package is available via pypi and you can easily test it out here if you wish.
-#
-# ```python
-# A_ES_ert = ies.ensemble_smoother_update_step(
-#     Y,
-#     A,
-#     obs_std[~is_outlier],
-#     obs_value[~is_outlier],
-#     inversion=ies.InversionType.EXACT,
-# )
-# ```
-
 # %% [markdown]
 # ## Numerical comparison of prior and posterior using RMSE
 #