[Docs] Removed metadata from incubating as its graduated feature

[axsaucedo]

Removed metadata from incubating as its graduated feature

What this PR does / why we need it:

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Does this PR introduce a user-facing change?:

[seldondev]

Thu Nov 5 11:12:56 UTC 2020
The logs for [pr-build] [1] will show after the pipeline context has finished.
https://github.com/SeldonIO/seldon-core/blob/gh-pages/jenkins-x/logs/SeldonIO/seldon-core/PR-2613/1.log

impatient try
jx get build logs SeldonIO/seldon-core/PR-2613 --build=1

[seldondev]

Thu Nov 5 11:13:00 UTC 2020
The logs for [lint] [2] will show after the pipeline context has finished.
https://github.com/SeldonIO/seldon-core/blob/gh-pages/jenkins-x/logs/SeldonIO/seldon-core/PR-2613/2.log

impatient try
jx get build logs SeldonIO/seldon-core/PR-2613 --build=2

[seldondev]

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