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: I987a7953b44ce27a93d0b29f3934a416bcdc93f2
Related-Bug: #1368910
Merge "Stop using intersphinx"