conf.py: remove deprecated get_html_theme_path()

Author: dhalbert

conf.py

@@ -277,7 +277,6 @@ def autoapi_prepare_jinja_env(jinja_env):
 
 import sphinx_rtd_theme
 html_theme = 'sphinx_rtd_theme'
-html_theme_path = [sphinx_rtd_theme.get_html_theme_path(), '.']
 
 # Theme options are theme-specific and customize the look and feel of a theme
 # further.  For a list of options available for each theme, see the