Revert "str: tune the pair from string parsing"

This reverts commit bc91e284.

Parser can't parse automata string inputs where a state containing a
pair is also a final state.

 NFA a b c d
 ><<(InitialStateLabel), 0> <a, 1> <b, 2> <c, 3> -
 <<a, 1> <a, 1> - - -
 <b, 2> - <b, 2> <c, 3> -
 <c, 3> - - - <d, 4>
 <<d, 4> - - - -