[Toybox] uniq --count

[enh]

i'm as in favor of long options as the next man (or significantly more
so, if the next man is Rob), but just for the record, i drew the line
at `uniq --count`. there was only one instance in the AOSP tree, so i
replaced it with `-c`.

a long option for `uniq -c` seems as crazy to me as a long option for
`ls -l` or `wc -l`... when it's core everyday functionality, a long
option makes no sense to me.

but if we're actually aiming for a consistent rule of "everything
that's been seen in the wild", i thought i should admit to having
hushed this one up :-)