boards: nrf9161dk_nrf9161: Remove TF-M not supported note

Remove note nrf9161dk_nrf9161 board stating that TF-M is not supported
for this board.

Signed-off-by: Joakim Andersson <joakim.andersson@nordicsemi.no>

Author: joerchan

boards/arm/nrf9161dk_nrf9161/doc/index.rst

@@ -138,9 +138,6 @@ have to set the IDAU (SPU) configuration to allow Non-Secure access to all
 CPU resources utilized by the Non-Secure application firmware. SPU
 configuration shall take place before jumping to the Non-Secure application.
 
-.. note::
-   Trusted Firmware-M (TF-M) and building the ``ns`` target is not supported for this board.
-
 Building a Secure only application
 ==================================