Fix wording in primops documentation to reflect the correct reasoning:
* Besides resizing functions, shrinking ones also mutate the
size of a mutable array and because of those two `sizeofMutabeByteArray`
and `sizeofSmallMutableArray` are now deprecated
* Change reference in documentation to then newer functions `getSizeof*`
instead of `sizeof*` for shrinking functions
* Fix incorrect mention of "byte" instead of "small"