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: Ie70e400478a092943a18f9f8595302380ec71cbc
Related-Bug: #1368910
Merge "Stop using intersphinx"