Remove PostgreSQL 14 specific upgrade command

The `gitlab-ctl pg-upgrade` command now defaults to PostgreSQL 14,
so it can be called without arguments to upgrade.

doc/settings/database.md

@@ -485,13 +485,6 @@ the upgrade:
 sudo gitlab-ctl pg-upgrade
 ```
 
-To upgrade to a specific PostgreSQL version, use the `-V` flag to append the
-version. For example, to upgrade to PostgreSQL 14:
-
-```shell
-sudo gitlab-ctl pg-upgrade -V 14
-```
-
 NOTE:
 `pg-upgrade` can take arguments; for example, you can set the timeout for the
 execution of the underlying commands (`--timeout=1d2h3m4s5ms`). Run `gitlab-ctl pg-upgrade -h`