Disable copyrighter for the time being, until further notice.

[soonkuk]

Expected Behavior

• Currently copyrighter is not necessary
• Copyrighter will be added when it is needed.

Actual Behavior

• Copyrighter is presented in code.

Steps to Reproduce the Problem

1. mitum-nft/nft/collection/mint_item.go

   Line 20 in 62a9cd3

   copyrighters nft.Signers

Specifications

• commit; 1b3d248
• os; macos ventura
• go version; go1.19