Fix logo transparency and remove duplicate from index page

- Process logo with ImageMagick to properly remove baked-in checkerboard
  background pattern and make it truly transparent
- Remove logo from docs/index.rst since html_logo already displays it
  in the Furo sidebar

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: laughingman7743

docs/_static/logo.png

@@ -1,10 +1,5 @@
 .. _pyathena:
 
-.. image:: _static/logo.png
-  :alt: PyAthena logo
-  :align: center
-  :width: 200
-
 PyAthena
 ========