remove depreciated line (#1882)

Author: Juan Orduz

docs/source/conf.py

@@ -7,7 +7,6 @@
 import sys
 
 import nbsphinx
-import sphinx_rtd_theme
 
 # import pkg_resources
 
@@ -227,7 +226,6 @@
 # a list of builtin themes.
 #
 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