Disable the rt flavours for armhf and arm64 as well

At the moment Apertis does not use the real-time kernels, so let's not waste
time on the builders.

Signed-off-by: Emanuele Aina <emanuele.aina@collabora.com>

debian/config/arm64/defines

@@ -2,7 +2,6 @@
 kernel-arch: arm64
 featuresets:
  none
- rt
 
 [build]
 debug-info: true

debian/config/armhf/defines

 [base]
 featuresets:
  none
- rt
 kernel-arch: arm
 
 [build]