Make non zero requirement for bond creation redundant, and remove it

[bingen]

In practice, we can still use 1e-18 if we don’t want to enforce a min value.

Fixes #222.

[danielattilasimon]

Why is this failing?

Failing tests:
Encountered 1 failing test in src/test/ChickenBondManagerDevTest.t.sol:ChickenBondManagerDevTest
[FAIL. Reason: Error != expected error: 'CBM: Bond minimum amount not reached' != 'CBM: Amount must be > 0'] testCreateBondRevertsWithZeroInputAmount() (gas: 40859)

[danielattilasimon]

Ah, I'm dumb, just need to update expected revert message in the test!