Remove unnecessary build steps.

Dockerfile

@@ -1,20 +1,12 @@
 # Build and base images are assumed to be based on the same major version of Debian.
 ARG build_image
 ARG base_image
-ARG protoc_version=3.15.3
 
 # Build stage.
 FROM ${build_image} AS build
 
 # Install system dependencies ('cmake' and 'g++' are dependencies of Rust crate 'prost-build').
-RUN apt-get update && apt-get install -y libssl-dev pkg-config cmake g++ wget zip && rm -rf /var/lib/apt/lists/*
-
-# Install protobuf compiler 'protoc'.
-ARG protoc_version
-RUN wget --no-verbose "https://github.com/protocolbuffers/protobuf/releases/download/v${protoc_version}/protoc-${protoc_version}-linux-x86_64.zip" \
-    && unzip "protoc-${protoc_version}-linux-x86_64.zip" \
-    && mv ./bin/protoc /usr/bin/protoc \
-    && chmod +x /usr/bin/protoc
+RUN apt-get update && apt-get install -y libssl-dev pkg-config && rm -rf /var/lib/apt/lists/*
 
 WORKDIR /build
 COPY . .