Logwrapper: Remove unused support for input / output processing.

Should make it easier to switch callers over to posix_spawn once
that's available.

NOTE: The (now) unused arguments will be removed in a followup (multi-project)c
hange once we empirically confirm that there aren't any prebuilt blobs
using this function. I did readelf all currently checked in prebuilts to look
for a reference to this method, but one can never be too paranoid.

Test: make checkbuild
Change-Id: I454d80c52f269c31846133cc54375decd702fe71