PalettedBlockArray::fromData() does not require any user input about bits-per-block

[dktapps]

Bits-per-block can be inferred from the size of the offset table (or $words), meaning that having this parameter at all is completely redundant.

The only thing bpb is required for is to know how many bytes to read when decoding palettes from disk, which is not something this extension has to care about. It only needs to care that the provided data is valid. This useless parameter is just providing an extra avenue for potential bugs.