More `decl_error!` migrations (#4427)

* Update assets to `decl_error`

* Update aura to `decl_error`

* Update authority discovery to `decl_error`

* Update collective to `decl_error`

* Update evm to `decl_error!`

* Fix error with replace

* Revert "Update authority discovery to `decl_error`"

This reverts commit 26e8f3c5.

* Revert "Update aura to `decl_error`"

This reverts commit 8f17c44c.

* Update democracy to `decl_error`

* Update finality-tracker to `decl_error`

* Update grandpa to `decl_error`

* `assert` to `ensure` in dispatchable function