This reverts commit 3e991230.

# Conflicts:
#	app/models/project.rb

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These sections were removed but:
- even if the NGINX config wasn't
modified, it might be in future updates so it's better to always have it
instead of having to remember to add it depending on the changes
- the init script update section must be there since it's a safe command
  line that should be run on every update

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Needed because of !2782.

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Fixes routing errors for /api/v3/projects/

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Closes https://github.com/gitlabhq/gitlabhq/issues/9904

The init script is already being updated in section 6.

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Update 8.0-to-8.1 update guide

- User needs to update gitlab-git-http-server
- User needs to update Nginx configuration

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See merge request !1625

Also adds a preamble note that a working 8.0 installation (i.e.,
gitlab-git-http-server, updated Nginx/Apache configs) is required before
proceeding.

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