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: Iade62023085dba8edca3ed62f53a2cb137d81c6d
Related-Bug: #1368910
Merge "Stop using intersphinx"