Figure: Remove the deprecated _preprocess method (Deprecated since v0.16.0) (#4146)

Author: seisman

pygmt/figure.py

@@ -4,7 +4,6 @@
 
 import base64
 import os
-import warnings
 from pathlib import Path
 from tempfile import TemporaryDirectory
 from typing import Literal, overload
@@ -120,21 +119,6 @@ def _activate_figure(self) -> None:
         with Session() as lib:
             lib.call_module(module="figure", args=[self._name, fmt])
 
-    # TODO(PyGMT>=v0.18.0):  Remove the _preprocess method.
-    def _preprocess(self, **kwargs):
-        """
-        Call the ``figure`` module before each plotting command to ensure we're plotting
-        to this particular figure.
-        """
-        self._activate_figure()
-        warnings.warn(
-            "The Figure._preprocess() method is deprecated since v0.16.0 and will be "
-            "removed in v0.18.0. Use Figure._activate_figure() instead.",
-            FutureWarning,
-            stacklevel=2,
-        )
-        return kwargs
-
     @property
     def region(self) -> np.ndarray:
         """