Stop using intersphinx

Remove intersphinx from the docs build as it triggers network calls that
occasionally fail, and we don't really use intersphinx (links other
sphinx documents out on the internet)

This also removes the requirement for internet access during docs build.

This can cause docs jobs to fail if the project errors out on
warnings.

Change-Id: I6d0bb0678ff35a751c0b7c40cb73803701eb8a75
Related-Bug: #1368910
Merge "Stop using intersphinx"