docs: Do not force alabaster theme

Sphinx will use the 'alabaster' theme by default when building locally. However,
Read the Docs will use their own theme by default which suits their site better.

By not specifying html_theme we allow both targets to use the appropriate
default theme.

Signed-off-by: Paul Barker <pbarker@toganlabs.com>

docs/conf.py

@@ -120,7 +120,7 @@ todo_include_todos = False
 # The theme to use for HTML and HTML Help pages.  See the documentation for
 # a list of builtin themes.
 #
-html_theme = 'alabaster'
+# html_theme = 'alabaster'
 
 # 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