Forgot that `ob-dot.el` exists in Org. I blindly expected the
`graphviz-dot-mode` package to provide babel support in f6b7e8a.
Also, `org-src-lang-modes` expects its CDRs to omit the -mode suffix,
which should fix syntax highlighting of graphviz/dot babel blocks.
Amend: f6b7e8ae48
Ref: #7546