docs: Removed support libraries from API Guide TOC

See (e.g.) TOC on http://go/dods-stage/guide/ to verify it.
Previously (e.g. on https://developer.android.com/guide/ )
you'd see a "Libaries" menu item between "Data Storage" and
"Administration"; that's gone now.

Already made this change in Critique (http://cr/134027548) but since
we're still publishing docs from Gerrit, thought it's best to
back-port this change.

bug: 31607475
Change-Id: I40ff0bebf76305dcad3ef0fc6fbe271b4a625a57