remove unnecessary container build steps

dockerfiles/alpine.Dockerfile

@@ -18,15 +18,8 @@ RUN \
   apk update -q; \
   apk add bash jemalloc
 
-RUN \
-  --mount=type=cache,id=usr-local-bundle-cache,target=${BUNDLE_PATH},sharing=locked \
-  gem update --system --no-document; \
-  gem install -N bundler
-
 FROM base AS build
 
-ARG TARGETARCH
-
 RUN \
   --mount=type=cache,id=var-cache-apk-${TARGETARCH},target=/var/cache/apk,sharing=locked \
   apk update -q; \

dockerfiles/bookworm.Dockerfile

@@ -23,18 +23,9 @@ RUN \
   apt-get install --yes --no-install-recommends \
   libjemalloc2
 
-RUN \
-  --mount=type=cache,id=usr-local-bundle-cache,target=${BUNDLE_PATH},sharing=locked \
-  gem update --system --no-document; \
-  gem install -N bundler
-
-ENV DEBIAN_FRONTEND="noninteractive"
-
 
 FROM base AS build
 
-ARG TARGETARCH
-
 RUN \
   --mount=type=cache,id=var-cache-apt-${TARGETARCH},target=/var/cache/apt,sharing=locked \
   --mount=type=cache,id=var-lib-apt-${TARGETARCH},target=/var/lib/apt,sharing=locked \