Don't cast histogram to int64 when density=True

[manopapad]

In that case the histogram is expected to have floating-point values, and casting those to ints drops information. E.g. this example:

import cunumeric as cn
data = cn.arange(20)
hist, _ = cn.histogram(data, density=True)
print(hist)

would print out

[0 0 0 0 0 0 0 0 0 0]

rather than

[0.05263158 0.05263158 0.05263158 0.05263158 0.05263158 0.05263158 0.05263158 0.05263158 0.05263158 0.05263158]