util: Remove linear_realloc()

util: Remove linear_realloc()

Now that linear_realloc() is unused, remove it.  It is not an actual
realloc, will always allocate new memory and copy data around -- and
had a big warning about it in the documentation.

In the couple of uses we had before, the client code knew the size,
so it could be changed to perform the allocation and the copy by
themselves.  The client code keeping the size is the recommended
way here.

This will allow us remove linear_size_chunk later.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25280>