Removes 'No DB maintainers available' section

Reverts a1c6a1d3. We have 5 DB
maintainers now on different timezones, even though the ratio of backend
engineers per database maintainer is still not great (163:5), the
chances of not having a maintainer available are fewer.

doc/development/database_review.md

@@ -45,13 +45,6 @@ A database **reviewer**'s role is to:
   reassign MR to the database **maintainer** suggested by Reviewer
   Roulette.
 
-#### When there are no database maintainers available
-
-Currently we have a [critical shortage of database maintainers](https://gitlab.com/gitlab-org/gitlab/issues/29717). Until we are able to increase the number of database maintainers to support the volume of reviews, we have implemented this temporary solution. If the database **reviewer** cannot find an available database **maintainer** then:
-
-1. Assign the MR for a second review by a **database trainee maintainer** for further review.
-1. Once satisfied with the review process and if the database **maintainer** is still not available, skip the database maintainer approval step and assign the merge request to a backend maintainer for final review and approval.
-
 A database **maintainer**'s role is to:
 
 - Perform the final database review on the MR.