memblock: Kill ARCH_POPULATES_NODE_MAP once more

The Kconfig symbol ARCH_POPULATES_NODE_MAP was killed in v3.3. After
that it popped up again in microblaze and metag. Nobody noticed,
probably because these Kconfig symbols are entirely unused and these
architectures both select HAVE_MEMBLOCK_NODE_MAP. Anyhow, these two
entries can also be killed.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Acked-by: Michal Simek <monstr@monstr.eu>
Signed-off-by: James Hogan <james.hogan@imgtec.com>