MAINTAINERS: remove maintainer-ship status for ioannisg

Removing maintainer and/or collaborator status on
- nRF platforms
- TF-M
- userspace
- cmsis-dsp
- MAINTAINERS file

for ioannisg. Replace with @anangl or others, where applicable.

Signed-off-by: Ioannis Glaropoulos <Ioannis.Glaropoulos@nordicsemi.no>