Revert "Gitlab::UrlBlocker: Ensure absence of URI scheme with `schemes: :none`"

What does this MR do and why?

This reverts commit 77870fca added in !115189 (merged).

According to https://www.ietf.org/rfc/rfc3986.txt URIs without a scheme are invalid. Weirdly, they are accepted by Addressable::URI.parse.

For example:

uri = Addressable::URI.parse("192.168.1.2")
uri.scheme   # => nil
uri.hostname # => nil
uri.path     # => "192.168.1.2

With this it doesn't make sense to enforce URI without a scheme when passing schemes: :none to UrlBlocker as it won't be able to resolve those URI because hostname is nil:

Gitlab::UrlBlocker.validate!("192.168.1.2", schemes: :none)
# Gitlab::UrlBlocker::BlockedUrlError: Host cannot be resolved or invali
# Caused by SocketError: getaddrinfo: Name or service not known

Note that the option schemes: :none isn't used in production and was only added to support !114917 (comment 1320128257) which isn't merged yet.

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