alarm: remove references to timezone

[ppannuto]

Use of timezone in {get/set}timeofday is deprecated.

If something did try to pass us the parameter, our implementation would (incorrectly) ignore it. More significantly, our implementation does not check that the timeval struct is nonnull before dereferencing it.

This updates libtock's interface to match our implementation and the common-case scenario, and leaves the question of what to do if something tries to use the legacy tz parameter to whomever implements the wrapper.