Clarify RJUMP in Stack Validation

[chfast]

The mega-spec eof.md explains successor instructions as follows:

3. Determine the list of successor instructions that can follow the current instructions:
   1. The next instruction for all instructions other than terminating instructions and RJUMP.
   2. All targets of a RJUMPI or RJUMPV.

There RJUMP is unspecified.

The EIP-5450 is better, but unconditional jump is actually never defined (neither in EIP-4200).

3. Determine the list of successor instructions that can follow the current instructions:
   1. The next instruction for all instructions other than terminating instructions and unconditional jump.
   2. All targets of a conditional or unconditional jump.