Clean up the solidity compilation warnings shown at compile time

[alsco77]

Is your feature request related to a problem? Please describe.
Run yarn compile and you will see a LOT of yellow warning text show up. Some of these are very very minor, some can potentially come into a larger issue.

Describe the solution you'd like
Resolve all of these warnings by modifying the solidity code, or add rules to the compiler to dismiss them, such that we have no warnings left when compilation happens.

Additional context
There is no real reason to receive warnings for the contracts in z_mocks since they are unused - these can simply be turned off.