feat: add launch pallet removal migration

[wischli]

fixes KILTProtocol/ticket#1951

• Removes the launch pallet
• Adds migration to kill all storage related to the KiltLaunch storage prefix 0x37be294ab4b5aa76f1df3f80e7c180ef

Checklist:

• I have verified that the code works
  • No panics! (checked arithmetic ops, no indexing array[3] use get(3), ...)
• I have verified that the code is easy to understand
  • If not, I have left a well-balanced amount of inline comments
• I have left the code in a better state
• I have documented the changes (where applicable)

[wischli]

This PR was automatically closed on accident by pushing to an incorrect branch (base). Reopened in #359