db: remove kvdb to sql migration from dev db stream

Remove the KVDB-to-SQL migration from the dev SQL migration set now
that this migration is now part of the production migration set.

As the migrations_dev folder no longer contains any migrations, we also
update the db logic and the gen_sqlc_docker.sh script to not error when
the folder(s) are empty.

scripts/gen_sqlc_docker.sh

@@ -1,6 +1,7 @@
 #!/bin/bash
 
 set -e
+shopt -s nullglob
 
 # restore_files is a function to restore original schema files.
 restore_files() {