Normative references section doesn't actually include any normative references

[timsong-cpp]

There should be a list, and the abbreviations (p2) probably should be in normative text rather than a note.

[jwakely]

This is being addressed in response to an NB comment on the PDTS ballot. See bd8ff6c on branch https://github.com/cplusplus/networking-ts/tree/pdts-ballot-resolutions