- bump the openstackdocstheme requirement to 1.20.0, the minimum
recommended version nowadays, and clean the configuration
by removing the options now provided by the theme;
- add the pdf-docs tox environment according the established guidelines;
- remove a useless extra title (for both builders);
- docs tox environment: clean up only the generated html, not the entire
build directory;
- disable the too smart smartquotes option for the latex builder;
- improve the title of the latex document.
Story: 2006117
Task: 35495
Change-Id: I353e33db27c8d676398973995960b98d3163aa0d