ipq806x: fix aliases node name for Qualcomm IPQ8064/DB149

ipq806x: fix aliases node name for Qualcomm IPQ8064/DB149

This device uses a node incorrectly named "alias" instead of
"aliases" since it was introduced.

Remove it without replacement, as the definitions in it don't
seem to be required anyway:

The serial0 definition has never been effective anyway and this
would be the only device deviating from the common setting
"serial0 = &gsbi4_serial;" for ipq8064. (So, maybe the wrong
node prevented us from finding out about the wrong serial
definition?)

The mdio-gpio0 alias was supposed to be removed in d2a2eb7e48f6
anyway, the redundant definition in the alias node was just
overlooked back then.

Fixes: 0fd202f3e563 ("ipq806x: add db149 dts files")
Fixes: d2a2eb7e48f6 ("ipq806x: replace caf nss-gmac driver by upstream stmmac")
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>