Remove golang v1.21, it's no longer available (#36)

Author: damyan

dev/Dockerfile

@@ -4,7 +4,7 @@ USER root
 
 RUN apt-get update \
   && apt-get install -y --no-install-recommends \
-    build-essential delve gdb golang-1.21-go golang-1.22-go golang-1.23-go make python3 python3-pip \
+    build-essential delve gdb golang-1.22-go golang-1.23-go make python3 python3-pip \
   && rm -rf /var/lib/apt/lists/*
 
 WORKDIR "/home/damyan"