DOC: Remove text rotation example

The content is duplicate to the "Text rotation mode" example and the
latter has a better and more complete description.

Author: timhoffm

examples/text_labels_and_annotations/demo_text_rotation_mode.py

@@ -17,6 +17,8 @@
   the bounding box of the rotated text.
 - ``rotation_mode='anchor'`` aligns the unrotated text and then rotates the
   text around the point of alignment.
+
+.. redirect-from:: /gallery/text_labels_and_annotations/text_rotation
 """
 
 import matplotlib.pyplot as plt