Update docker image build

Dockerfile

@@ -12,12 +12,7 @@ WORKDIR /src
 
 COPY go.mod .
 
-# See: https://docs.docker.com/develop/develop-images/build_enhancements/
-# http://blog.oddbit.com/post/2019-02-24-docker-build-learns-about-secr/
-RUN --mount=type=ssh,id=github git config --global url."git@github.com:".insteadOf "https://github.com/"; \
-    mkdir -p -m 0600 ~/.ssh && ssh-keyscan github.com >> ~/.ssh/known_hosts; \
-    go env -w GOPRIVATE="github.com/SB-IM"; \
-    go mod download all; \
+RUN go mod download all; \
     go mod verify
 
 COPY . .

Makefile

@@ -1,8 +1,3 @@
-# SSH private key set up.
-CURRENT_USER ?= $(shell whoami)
-PRIVATE_KEY_FILE ?= id_ed25519
-PRIVATE_KEY_PATH ?= github=${HOME}/.ssh/$(PRIVATE_KEY_FILE)
-
 # Enable docker buildkit.
 DOCKER_BUILDKIT = 1
 # Project image repo.
@@ -55,7 +50,6 @@ image:
 	@docker build \
 	--build-arg DEBUG=$(DEBUG) \
 	--build-arg BUILD_TAGS=$(BUILD_TAGS) \
-	--ssh $(PRIVATE_KEY_PATH) \
 	-t $(IMAGE_REPO):$(IMAGE_TAG)-$(BUILD_TAGS) \
 	.