Remove repeated routes.path check for postgresql database

What does this MR do?

Remove repeated routes.path comparison for postgresql database. Before:

SELECT "projects".*
FROM "projects"
INNER JOIN "routes" ON "routes"."source_id" = "projects"."id"
AND "routes"."source_type" = 'Project'
WHERE "projects"."pending_delete" = 'f'
  AND (((routes.path = 'gitlab-org/gitlab-ci')
        OR (LOWER(routes.path) = LOWER('gitlab-org/gitlab-ci'))))
ORDER BY (CASE
              WHEN routes.path = 'gitlab-org/gitlab-ci' THEN 0
              ELSE 1
          END)
LIMIT 1

After:

SELECT "projects".*
FROM "projects"
INNER JOIN "routes" ON "routes"."source_id" = "projects"."id"
AND "routes"."source_type" = 'Project'
WHERE "projects"."pending_delete" = 'f'
  AND ((LOWER(routes.path) = LOWER('gitlab-org/gitlab-ci')))
ORDER BY (CASE
              WHEN routes.path = 'gitlab-org/gitlab-ci' THEN 0
              ELSE 1
          END)
LIMIT 1

Are there points in the code the reviewer needs to double check?

• I didn't use CaseSensitivity#iwhere because it'll return a result.

where_full_path_in could be simplified to something like

      if paths.empty?
        none
      else
        if cast_lower
          joins(:route).where(routes[:path].lower.in(paths.map(&:downcase)))
        else
          joins(:route).where(routes[:path].in(paths))
        end
      end

I find the above implementation simpler/easier to read, but that's just my opinion.

Why was this MR needed?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?