remove unused structs in indexer db models

[mariajdab]

We can use the sqlc tag omit_unused_structs: true to avoid create models that are not being used in any part of the code

[coveralls]

Pull Request Test Coverage Report for Build 6648385844

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.009%) to 62.197%

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Files with Coverage Reduction	New Missed Lines	%
vochain/state/cache.go	2	61.54%

Totals
Change from base Build 6646214448:	-0.009%
Covered Lines:	14092
Relevant Lines:	22657

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💛 - Coveralls