This code was no longer needed after switching to os_read_file, but I
accidentally left it around, whoops!
Fixes: 49183bfb79 ("pan/bi: use os_read_file-helper")
CID: 1665295
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Lars-Ivar Hesselberg Simonsen <lars-ivar.simonsen@arm.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37903>