docs: remove the original doc-ci.yml action as it's output is now unu…

…sed (#5250)

Rename the newer docs-ci-v2 as just docs-ci.yml. The website now only uses output from the newer action. I made no changes other delete and rename.

Note: I've left that rsynced path as deephaven-core-v2/ on the server, as that's where all the symlinks point and I am being lazy and don't want to have to co-ordinate swapping that live.