MAINTAINERS: Remove myself as SiLabs collaborator

I am not using Silicon Labs platform for a while now and will not be for
the foreseeable future.

Signed-off-by: Christian Taedcke <[email protected]>

Author: chrta

MAINTAINERS.yml

@@ -1757,8 +1757,6 @@ Nuvoton Numicro Platforms:
 
 SiLabs Platforms:
   status: odd fixes
-  collaborators:
-    - chrta
   files:
     - soc/arm/silabs_*/
     - boards/arm/ef*/
@@ -2340,7 +2338,6 @@ West:
   collaborators:
     - yonsch
     - mnkp
-    - chrta
   files:
     - modules/Kconfig.silabs
   labels: