Rename OP_INVALIDOPCODE to drop the "OP".

As some people add this to the SPEC based on the fact that it starts with the OP_, lets make this absolutely clear that we do not have support for this "opcode".

Spec: https://github.com/SoftwareVerde/bitcoin-cash-specification/blob/master/protocol/blockchain/script.md#node-specific-behavior

Test plan: ninja check check-functional (added by @BigBlockIfTrue)