maintainers: drop gmarull as collaborator from a few areas

I won't be available to collaborate in MFD, Input or GD32 areas, so
let's drop my collaborator entries.

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>

Author: gmarull

MAINTAINERS.yml

@@ -1822,7 +1822,6 @@ Release Notes:
 "Drivers: MFD":
   status: odd fixes
   collaborators:
-    - gmarull
     - aasinclair
   files:
     - drivers/mfd/
@@ -2392,8 +2391,6 @@ Input:
   status: maintained
   maintainers:
     - fabiobaltieri
-  collaborators:
-    - gmarull
   files:
     - doc/services/input/
     - drivers/input/
@@ -3487,7 +3484,6 @@ GD32 Platforms:
   maintainers:
     - nandojve
   collaborators:
-    - gmarull
     - soburi
     - cameled
   files:
@@ -4949,7 +4945,6 @@ West:
   maintainers:
     - nandojve
   collaborators:
-    - gmarull
     - soburi
   files:
     - modules/hal_gigadevice/