remove other tick count masking

not needed because count wraps from 0x7FFFFFFF to 0x80000000
and from 0xFFFFFFFF to 0x00000000 and a simple subtract gives
correct result in any case

also some of the subtracts were incorrect because:

    delta = (newcount & 0x7FFFFFFF) - (oldcount & 0x7FFFFFFF)

    yields incorrect delta result when for example
    oldcount = 0x7FFFFFFF and newcount = 0x80000000