powerpc/603: Remove outdated comment

Since commit 84de6ab0

 ("powerpc/603: don't handle PAGE_ACCESSED
in TLB miss handlers.") page table is not updated anymore by
TLB miss handlers.

Remove the comment.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/38b1ffefd2146fa56bf8aa605d476ad9736bbb37.1643613296.git.christophe.leroy@csgroup.eu