Always use uint8 for t2count and reverseH in buildBinaryFuse

[RaduBerinde]

The values stored in these slices are independent of the fingerprint
size. It looks like maybe a mistake when the code was converted to use
generics.

This improves build performance a bit (and reduces mem usage) for
16-bit fingerprints. On an M1 laptop:

name                                old time/op    new time/op    delta
BinaryFusePopulate/16/n=1000000-10    29.4ms ± 1%    28.1ms ± 1%  -4.25%  (p=0.000 n=10+10)

name                                old MKeys/s    new MKeys/s    delta
BinaryFusePopulate/16/n=1000000-10      34.1 ± 1%      35.6 ± 1%  +4.44%  (p=0.000 n=10+10)

name                                old alloc/op   new alloc/op   delta
BinaryFusePopulate/16/n=1000000-10    28.1MB ± 0%    26.0MB ± 0%  -7.58%  (p=0.000 n=8+9)

name                                old allocs/op  new allocs/op  delta
BinaryFusePopulate/16/n=1000000-10      8.00 ± 0%      8.00 ± 0%    ~     (all equal)

[lemire]

Very nice.