Optimize Alpine Dockerfile by removing redundant apk commands (#5016)

Remove unnecessary `apk update` and manual cache cleanup steps in the
Alpine Dockerfile. By using `apk add --no-cache`, we avoid manual cache
management, making the Dockerfile simpler and easier to maintain.

docker/Dockerfile.alpine

@@ -11,9 +11,7 @@ FROM $LITELLM_BUILD_IMAGE AS builder
 WORKDIR /app
 
 # Install build dependencies
-RUN apk update && \
-    apk add --no-cache gcc python3-dev musl-dev && \
-    rm -rf /var/cache/apk/*
+RUN apk add --no-cache gcc python3-dev musl-dev
 
 RUN pip install --upgrade pip && \
     pip install build