[POWERPC] Remove dead code for preventing pread() and pwrite() calls

Remove the deactivated code for checking for pread() and pwrite()
calls on the PPC-based BRIQ.

Signed-off-by: Robert P. J. Day <rpjday@mindspring.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>