powerpc/40x: Remove stale PTE_ATOMIC_UPDATES macro

40x TLB handlers were reworked by commit 2c74e258 ("powerpc/40x:
Rework 40x PTE access and TLB miss") to not require PTE_ATOMIC_UPDATES
anymore.

Then commit 4e1df545 ("powerpc/pgtable: Drop PTE_ATOMIC_UPDATES")
removed all code related to PTE_ATOMIC_UPDATES.

Remove left over PTE_ATOMIC_UPDATES macro.

Fixes: 2c74e258

 ("powerpc/40x: Rework 40x PTE access and TLB miss")
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/f061db5857fcd748f84a6707aad01754686ce97e.1695659959.git.christophe.leroy@csgroup.eu