chore: remove creation of nft collection from LM migration

[martinfridrich]

Creation of NFT collection for xyk LM pallet was removed from migration. This collection is already exists on Rococo and Basilisk.

[github-actions]

Crate versions that have not been updated:

• pallet-xyk: v6.0.0

Crate versions that have been updated:

• pallet-xyk-liquidity-mining: v1.0.0 -> v1.0.1

Runtime version has not been increased.

[codecov]

Codecov Report

Base: 80.23% // Head: 80.30% // Increases project coverage by +0.07% 🎉

Coverage data is based on head (7057dc6) compared to base (377024d).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #572      +/-   ##
==========================================
+ Coverage   80.23%   80.30%   +0.07%     
==========================================
  Files          25       25              
  Lines        2606     2595      -11     
==========================================
- Hits         2091     2084       -7     
+ Misses        515      511       -4     

Impacted Files	Coverage Δ
pallets/xyk-liquidity-mining/src/migration.rs	36.36% <ø> (-9.10%)	⬇️

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