samples subsys mgmt/updatehub: Do not enable POSIX_API

This sample does not use or need this component.
Let's not enable it.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>

Author: aescolar

samples/subsys/mgmt/updatehub/prj.conf

@@ -16,7 +16,6 @@ CONFIG_COAP=y
 CONFIG_DNS_RESOLVER=y
 CONFIG_JSON_LIBRARY=y
 CONFIG_HWINFO=y
-CONFIG_POSIX_API=y
 
 # Turn on the updatehub
 CONFIG_UPDATEHUB=y