Exclude Mark Karpov from ‘stackbuilders’ group

Soon I'll stop working for Stack Builders thus I remove myself from the ‘stackbuilders’ group. I still would like to be notified about ‘stache’-related issues, so I add that under my own name.

build-constraints.yaml

@@ -2169,6 +2169,7 @@ packages:
         - lame
         - path
         - forma
+        - stache
 
     # "Thomas Bereknyei <tomberek@gmail.com>":
         # - multiplate # bounds: transformers
@@ -3902,7 +3903,6 @@ github-users:
         - sestrella
         - jsl
         - jsantos17
-        - mrkkrp
     scotty-web:
         - RyanGlScott
         - xich