This partially reverts be25bbc4.
Signed-off-by: NRémy Coutable <remy@rymai.me>

New Gitlab::UrlSanitizer.http_credentials_for_user method responsible
for generating a credentials hash from a user.
Signed-off-by: NRémy Coutable <remy@rymai.me>

The API was returning 500 when `nil` is passed for the `import_url`.

In fact, it was `Gitlab::UrlSanitizer.valid?` which was throwing a
`NoMethodError` when `nil` value was passed.

This reverts commit 3e991230.

# Conflicts:
#	app/models/project.rb