Minor reformatting, remove broken Sphinx markup

Author: tekktrik

displayio_cartesian.py

@@ -504,7 +504,6 @@ def _add_point(self, x: int, y: int) -> None:
         :param int x: ``x`` coordinate in the local plane
         :param int y: ``y`` coordinate in the local plane
         :return: None
-        rtype: None
         """
 
         local_x, local_y = self._calc_local_xy(x, y)
@@ -566,6 +565,7 @@ def _add_point(self, x: int, y: int) -> None:
                             self.height,
                         )
                     )
+
         else:
             # for better error messages we check in detail what failed...
             if not self._check_x_in_range(x):
@@ -644,8 +644,6 @@ def clear_plot_lines(self, palette_index=5):
 
         :param int palette_index: color palett index. Defaults to 5
         :return: None
-
-        rtype: None
         """
         self.plot_line_point = None
         self._plot_bitmap.fill(palette_index)