macro: sizeof() returns size_t, and that's good

macro: sizeof() returns size_t, and that's good

Now that CONST_MAX() is a bit more foregiving, let's stick to the native
return type of sizeof() everywhere, which is size_t, instead of casting
to "unsigned", so that on the common archs we don't unnecessarily lose
the upper 32bits.

This semi-reverts d3e40294572512810c9329933a488619e7ce22fd.