OPCM: unify assertValidContractAddress

[zhiqiangxu]

This PR replaces the OPCM.assertValidContractAddress with DeployUtils.assertValidContractAddress, which makes it more consistent.

(OPCM is the only contract that defines its own assertValidContractAddress function)

[maurelian]

Overall this LGMT and it's great to reduce redundancy.

But I have some reservations about pulling in code from a lib called DeployUtils which is stored in scripts.

I think I'd prefer to move this out of DeployUtils into something in src/libraries. Either in an existing library if a relevent one exists (nothing looked immediately obvious), or a new one if necessary.

[maurelian]

/ci authorize ca0088e

[tynes]

Generally agree that pulling in something from scripts into something that lives onchain is a leaky abstraction. Altho we are doing "onchain scripting". Generally onboard with abstracting this into a library, feels pretty similar to the OZ isContract function

[zhiqiangxu]

Btw isContract has been removed: OpenZeppelin/openzeppelin-contracts#3945

Looks like the OZ way is to just check the length.