remove redundant \expandafter definition

[dginev]

Spotted while porting. There appear to be two \expandafter definitions following each other.

As the first one wasn't getting used (immediately overwritten by the second), this PR removes it for clarity.

[dginev]

I also removed a redundant \relpenalty (TeXbook value seems to be 500)

[dginev]

There are also two definitions of \newread and \newwrite in plain.pool.ltxml, but I am not sure which of the two variants should be kept? May be worth a look.

[brucemiller]

I'll have to remember to take a look at \newread & \newrite, as there are some subtle differences between plain.tex and plain.pool approaches which need sorting.

[brucemiller]

Looks good; thanks!