Tests for branch in delay slot are incomplete (and not needed)

[BlocksOnAChain]

Description
The test if (_cpu.nextPC != _cpu.pc + 4), used to detect if there is a jump in the delay slot, has 2 problems:

Will not detect that there is a jump in the delay slot if the previous instruction was a jump to pc + 8;
Is not strictly needed, given the assumption that the guest code is trusted (i.e. that it will not try to exploit differences between this and other MIPS implementations to cause the execution to diverge).\

Recommendation:
Remove the tests.

packages/contracts-bedrock/src/cannon/libraries/MIPS64Instructions.sol
if (_cpu.nextPC != _cpu.pc + 4) {
packages/contracts-bedrock/src/cannon/libraries/MIPS64Instructions.sol
if (_cpu.nextPC != _cpu.pc + 4) {