[Fix] Make sure pool metadata is removed on pool dissolve (#12154)

* [Fix] Make sure pool metadata is removed on pool dissolve

* add migration

* remove_metadata helper removed

* fix typo and add a comment

* fix pre_upgrade

* fix migration

* Update frame/nomination-pools/src/migration.rs

Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

* Update frame/nomination-pools/src/migration.rs

Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

* address comments

* fix comments

* Update frame/nomination-pools/src/migration.rs

Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

* address comments

* permissions fix

Co-authored-by: parity-processbot <>
Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>