ARM: dts: aspeed: Rainier 4U: Remove fan updates

The 4U fans do not need a different "tach-pulses" property than the 2U
machine. In addition, the "maxim,fan-dual-tach" property does not exist
upstream yet, so it should also be removed.

Signed-off-by: Eddie James <eajames@linux.ibm.com>
Signed-off-by: Joel Stanley <joel@jms.id.au>