Remove Purchase Pallet from Polkadot + Westend (#1636)

* Remove purchase pallet

* Update runtime/common/src/purchase.rs

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* Actually check and fix compile

* Add events to dummy

* Fix kusama too

* remove events where it did not exist historically

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>
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