dts: nordic: nrf9160: Remove redundant aliases

Several aliases were added to nrf9160[ns].dtsi files solely for
the purpose of getting base addresses of certain hardware modules
via DT_ macros generated for these aliases.
Since for one-instance modules the same can be now achieved with
standard DT_INST_0_* macros, there is no need to keep these aliases.

Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>