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: I1a0836c12fee97a5192aa40f5c2948809d009ae9
Related-Bug: #1368910
Merge "Stop using intersphinx"