dev(ssj): move `MockContractUpgradeableV1` and delete test_upgradeable.cairo

[enitrat]

Following #1558 we don't need test_upgradeable.cairo.

Move MockContractUpgradeableV1 outside of this file, but starknet-foundry still needs to be able to resolve the contract class, as it's used in test_kakarot_core.cairo.

[SoarinSkySagar]

Hi @enitrat, would like to be assigned to this issue and resolve it