conf.py: remove unused html_theme_path configuration

Per build warning;
WARNING: Calling get_html_theme_path is deprecated.
If you are calling it to define html_theme_path, you are safe to remove that code.

So removing the code to get rid of warning.

Signed-off-by: Christopher Turner <christopher.g.turner@intel.com>

Author: cgturner1

conf.py

@@ -132,7 +132,6 @@
     sys.stderr.write('Warning: sphinx_rtd_theme missing. Use pip to install it.\n')
 else:
     html_theme = "sphinx_rtd_theme"
-    html_theme_path = [sphinx_rtd_theme.get_html_theme_path()]
     html_theme_options = {
         'canonical_url': '',
         'analytics_id': 'GTM-M4BL5NF',